There's a computer game called The Sims 3 that's what they call a life simulator; the little pixel people eat and sleep and get married and have babies ... and they also get jobs. There are eleven expansion packs for the game, of which Into the Future is the most recent. Well, if there's a whole expansion pack devoted to life in the future, it needs to have Starfleet in it, right? Well, now it does, because I've made a Starfleet career as a mod for the game. :-)
You can get the career at http://nene.modthesims.info/download.php?t=580458. The mod is completely free, though it does take The Sims 3 and the Into the Future expansion pack to play. It's based on TOS, so you'll see occasional references to Kirk, Spock, McCoy or Scotty, and the uniforms and career path are all TOSian in flavor.
Writing the text for the career levels, career opportunities, career events, and so on was more difficult that it might seem at first, because the proper tone for a Sims career -- based on the other careers in the game -- is mildly humorous and slightly snarky, whereas the proper tone for TOS is earnest and idealistic, and those tones don't mesh terribly well. I tried to give Starfleet a Sims spin without totally disrespecting the source material; I hope players will like it.
Since unfortunately Starfleet doesn't exist in the present day, this career is only available in the future – it's based out of the Stellar Observatory rabbithole – so you'll need the Into the Future expansion pack to play it.
Like all fan-made careers, this one requires the Nraas Career mod, or the career won't exist in your game. You can get the Nraas Career mod at http://nraas.wikispaces.com/Careers.
OVERVIEW
You can get the job by using a computer once you go to Oasis Landing (the future world in Into the Future), or you can go to the Stellar Observatory rabbithole and apply directly there.

The career levels are job descriptions, not just ranks. I figure the progression of Ensign - Lieutenant - Lieutenant Commander - Commander - Captain is not all that interesting; what's interesting is what FUNCTION your sim has in Starfleet. So that's what I gave you. :-)
The Starfleet career has two branches – the Command track or the Science and Ship's Services track – and you get to choose a track when you're promoted to 5th level. The Command track uses only base-game and Into the Future skills, so if you have Into the Future, you can play that track.
The Science and Ship's Services track also uses skills that came with Ambitions and University Life, so you'll need those two expansion packs to play that track. (If you don't have the necessary EP's, please don't try to play the Science track, or your sim's skill list will get messed up.)
There are custom tones for this career, including skill-building tones for both the base career and each branch.
There are a LOT of career events and career opportunities included with this career, and by "a lot," I mean 34 of them! They're weighted to come up quite often, so you should get a career event or opportunity nearly every day.
There are custom uniforms for this career, based on the uniforms of the original series.
LEVELS
For the first two levels, you'll be a student at Starfleet Academy; for levels 3 - 8, you'll be serving on a ship, and for levels 9 and 10, you'll be serving in a ground-based position. If you don't want to leave the ship, then don't learn the skills you need for promotion to Level 9, and you'll get to stay on the ship a bit longer. :-)
The Redshirt level is designed to be dangerous but NOT lethal:

Levels 3 - 6 assume that you're serving on the Enterprise, under Captain Kirk and Mr. Spock. Once you reach either First Officer or Science Officer (depending on your track), the career assumes that you've transferred to another ship, since those positions are already filled on the Enterprise. Once at that level, the captain will be the same gender as your sim, so opportunities or events that refer to the captain will use "he" for male sims and "she" for female sims.
Some people like to know everything before they sign up for a career, whereas others think that being surprised is half the fun, so I've put the career levels under a cut tag. You can peek or not, as pleases you.
BRANCHES
This career is designed to let you grow up to be Kirk or Spock, and even to go beyond them, into job levels that are more appropriate for older sims (because you probably don't want to be getting into fist fights when you're 70. :-D) There's no way to grow up to be Scotty or McCoy, because their jobs require the specialized training of an entire track apiece, so including them would require FOUR career branches ... and the game engine doesn't allow that. :-)
If you decide to go for the Science and Ship's Services Track, you'll need the University Life and Ambitions expansion packs, in addition to Into the Future, because that track uses the Science skill that came with University Life EP and the Inventing skill that came with the Ambitions EP. (Spock knows how to do almost everything there is, so if you're going to grow up to be him, you'll have to learn a heck of a lot. But there are opportunities and events to help you!)
Please do NOT try to take the Science track if you don't have the necessary EP's, since that will mess up your sim's skill list! The Command track uses only base game and Into the Future skills, so you can still play the career even if you don't have Ambitions and University Life.
It wouldn't all fit in one message, so more in the next one!
You can get the career at http://nene.modthesims.info/download.php?t=580458. The mod is completely free, though it does take The Sims 3 and the Into the Future expansion pack to play. It's based on TOS, so you'll see occasional references to Kirk, Spock, McCoy or Scotty, and the uniforms and career path are all TOSian in flavor.
Writing the text for the career levels, career opportunities, career events, and so on was more difficult that it might seem at first, because the proper tone for a Sims career -- based on the other careers in the game -- is mildly humorous and slightly snarky, whereas the proper tone for TOS is earnest and idealistic, and those tones don't mesh terribly well. I tried to give Starfleet a Sims spin without totally disrespecting the source material; I hope players will like it.
Since unfortunately Starfleet doesn't exist in the present day, this career is only available in the future – it's based out of the Stellar Observatory rabbithole – so you'll need the Into the Future expansion pack to play it.
Like all fan-made careers, this one requires the Nraas Career mod, or the career won't exist in your game. You can get the Nraas Career mod at http://nraas.wikispaces.com/Careers.
OVERVIEW
You can get the job by using a computer once you go to Oasis Landing (the future world in Into the Future), or you can go to the Stellar Observatory rabbithole and apply directly there.

The career levels are job descriptions, not just ranks. I figure the progression of Ensign - Lieutenant - Lieutenant Commander - Commander - Captain is not all that interesting; what's interesting is what FUNCTION your sim has in Starfleet. So that's what I gave you. :-)
The Starfleet career has two branches – the Command track or the Science and Ship's Services track – and you get to choose a track when you're promoted to 5th level. The Command track uses only base-game and Into the Future skills, so if you have Into the Future, you can play that track.
The Science and Ship's Services track also uses skills that came with Ambitions and University Life, so you'll need those two expansion packs to play that track. (If you don't have the necessary EP's, please don't try to play the Science track, or your sim's skill list will get messed up.)
There are custom tones for this career, including skill-building tones for both the base career and each branch.
There are a LOT of career events and career opportunities included with this career, and by "a lot," I mean 34 of them! They're weighted to come up quite often, so you should get a career event or opportunity nearly every day.
There are custom uniforms for this career, based on the uniforms of the original series.
LEVELS
For the first two levels, you'll be a student at Starfleet Academy; for levels 3 - 8, you'll be serving on a ship, and for levels 9 and 10, you'll be serving in a ground-based position. If you don't want to leave the ship, then don't learn the skills you need for promotion to Level 9, and you'll get to stay on the ship a bit longer. :-)
The Redshirt level is designed to be dangerous but NOT lethal:

Levels 3 - 6 assume that you're serving on the Enterprise, under Captain Kirk and Mr. Spock. Once you reach either First Officer or Science Officer (depending on your track), the career assumes that you've transferred to another ship, since those positions are already filled on the Enterprise. Once at that level, the captain will be the same gender as your sim, so opportunities or events that refer to the captain will use "he" for male sims and "she" for female sims.
Some people like to know everything before they sign up for a career, whereas others think that being surprised is half the fun, so I've put the career levels under a cut tag. You can peek or not, as pleases you.
Career Levels
1. Plebe M,T,W,R,F 7 am - 3 pm §5/hour
Train your body and your mind, learn huge amounts of information, pass physical, mental, and psychological tests. Only the very best make it through the first year of Starfleet Academy!
2. Cadet M,T,W,R,F 7 am - 2 pm §10/hour
Continue to train your body and your mind. Learn all you can, because you never know what obscure fact or skill might save your life out there in the black.
3. Redshirt M,T,W,R,F 8 am - 2 pm §40/hour
You've graduated from the Academy and are now serving on a starship!
As a member of the Security team, it's your job to protect your captain on landing parties, guard dangerous prisoners on the ship, and generally get between trouble and the more important members of the crew.
Show a talent for survival (and for repairing broken machinery) if you want to be promoted.
4. Engineering Lad or Lass M,T,W,R,F 8 am - 2 pm §50/hour
You're the chief engineer's favorite minion, which means you get to monitor, maintain, and repair the engines. Hope you like getting your hands dirty, crawling through Jeffries tubes, and being sworn at in a Scottish accent.
COMMAND Track:
5. Navigator M,T,W,R,F 8 am - 2 pm §60/hour
You serve on the bridge now! This is where the action is.
Implementing the captain's orders about which course to follow is your responsibility. You don't want to end up on the wrong side of the Neutral Zone or in the heart of a star, so plot those courses carefully.
6. Helmsman M,T,W,R,F 8 am - 2 pm §75/hour
Piloting something as a big as a starship takes a good eye, steady nerves, and a thorough grasp of the laws of physics. Get good at evasive maneuvers if you want to live long enough to be promoted.
7. First Officer M,T,W,R,F 8 am - 3 pm §100/hour
It's the captain's job to focus on the mission and your job to keep the ship running smoothly so that everything he needs is ready whenever he needs it.
That means you get to handle everything from crew schedules to discipline to the procurement of resources. Plus, you get to go on landing parties to back up the captain whenever necessary.
Hope you don't need much sleep, because this is a BIG job!
8. Captain M,T,W,R,F 8 am - 3 pm §150/hour
You're an explorer, a diplomat, a cop, and a rescuer. You're the highest authority and the only recourse for hundreds of light years. That means you get to respond to emergencies on Federation planets, engage in high-level diplomacy with planets both allied and unallied, protect and defend Federation ships, planets, and personnel ... and squeeze in some exploration whenever you can. This can be a lonely job, but an astonishingly satisfying one.
9. Admiral M,T,W,R,F 9 am - 3 pm §300/hour
You let them promote you off the bridge of your ship, and now you fly a desk. But you get to make policy and bring all of your experience and know-how to the creation of that policy, so future starship captains will be guided by admirals who actually understand what it's like out there.
This is a good position for an older sim ... but part of your heart will always be out there in the black.
10. Commander in Chief, Starfleet M,T,W,R,F 10 am - 3 pm §500/hour
You're in charge of the whole thing; the buck really does stop here. You set the direction for hundreds of ships and thousands of people, using all of your experience and wisdom to make Starfleet's future ever better and brighter. Go ahead, implement your vision!
SCIENCE AND SHIP'S SERVICES Track:
5. Communications Officer M,T,W,R,F 8 am - 2 pm §60/hour
You serve on the bridge now! This is where the action is.
Incoming orders from Starfleet, outgoing reports from the captain, negotiations with alien ships, greetings to new planets, calls for help from landing parties ... it all goes through you.
Open those hailing frequencies and listen hard!
6. Computer Specialist M,T,W,R,F 8 am - 2 pm §70/hour
The computer controls the ship – everything from the helm to phasers to life support is computerized – so this is a key job. Do it well, and the captain and first officer will notice. Work on your logic and science skills if you'd like a position with more variety.
7. Astrophysicist M,T,W,R,F 8 am - 2 pm §85/hour
From star mapping to the analysis of nebulae, your job is to study the stellar objects all around you. You'll be expected to help the ship steer clear of black holes ... except when the captain wants to go back in time and has to slingshot around one for energy.
The rest of the crew may LOOK at stars, but you get to KNOW them.
8. Science Officer M,T,W,R,F 8 am - 3 pm §100/hour
You have information on every possible subject at your fingertips, the better to inform and advise the captain. You also manage all of the specialist scientists under your command, since as a generalist, only you have the knowledge to see how all those specialties fit together.
This may be the most intellectually satisfying job in Starfleet, except possibly for Head of Starfleet Research.
9. Instructor at Starfleet Academy M,T,W,R,F 7 am - 1 pm §200/hour
Science officer was a fun job, but it WAS a bit strenuous. As you age, it becomes your responsibility – and your privilege – to train the next generation of Starfleet officers.
It's hard to believe that you were ever this young and naive, but the next cohort of Starfleet officers comes from the kids you're teaching now!
10. Head of Starfleet Research M,T,W,R,F 10 am - 3 pm §400/hour
You know more about Science and Advanced Tech than anyone, which means you know where the gaps are. This makes you ideally suited to determine the overall research direction of every starship in the fleet AND to direct the groundside tech development that produces new and upgraded equipment for the people out there in the black.
You direct thousands of scientists on hundreds of ships and worlds; the future of Science herself is in your hands.
1. Plebe M,T,W,R,F 7 am - 3 pm §5/hour
Train your body and your mind, learn huge amounts of information, pass physical, mental, and psychological tests. Only the very best make it through the first year of Starfleet Academy!
2. Cadet M,T,W,R,F 7 am - 2 pm §10/hour
Continue to train your body and your mind. Learn all you can, because you never know what obscure fact or skill might save your life out there in the black.
3. Redshirt M,T,W,R,F 8 am - 2 pm §40/hour
You've graduated from the Academy and are now serving on a starship!
As a member of the Security team, it's your job to protect your captain on landing parties, guard dangerous prisoners on the ship, and generally get between trouble and the more important members of the crew.
Show a talent for survival (and for repairing broken machinery) if you want to be promoted.
4. Engineering Lad or Lass M,T,W,R,F 8 am - 2 pm §50/hour
You're the chief engineer's favorite minion, which means you get to monitor, maintain, and repair the engines. Hope you like getting your hands dirty, crawling through Jeffries tubes, and being sworn at in a Scottish accent.
COMMAND Track:
5. Navigator M,T,W,R,F 8 am - 2 pm §60/hour
You serve on the bridge now! This is where the action is.
Implementing the captain's orders about which course to follow is your responsibility. You don't want to end up on the wrong side of the Neutral Zone or in the heart of a star, so plot those courses carefully.
6. Helmsman M,T,W,R,F 8 am - 2 pm §75/hour
Piloting something as a big as a starship takes a good eye, steady nerves, and a thorough grasp of the laws of physics. Get good at evasive maneuvers if you want to live long enough to be promoted.
7. First Officer M,T,W,R,F 8 am - 3 pm §100/hour
It's the captain's job to focus on the mission and your job to keep the ship running smoothly so that everything he needs is ready whenever he needs it.
That means you get to handle everything from crew schedules to discipline to the procurement of resources. Plus, you get to go on landing parties to back up the captain whenever necessary.
Hope you don't need much sleep, because this is a BIG job!
8. Captain M,T,W,R,F 8 am - 3 pm §150/hour
You're an explorer, a diplomat, a cop, and a rescuer. You're the highest authority and the only recourse for hundreds of light years. That means you get to respond to emergencies on Federation planets, engage in high-level diplomacy with planets both allied and unallied, protect and defend Federation ships, planets, and personnel ... and squeeze in some exploration whenever you can. This can be a lonely job, but an astonishingly satisfying one.
9. Admiral M,T,W,R,F 9 am - 3 pm §300/hour
You let them promote you off the bridge of your ship, and now you fly a desk. But you get to make policy and bring all of your experience and know-how to the creation of that policy, so future starship captains will be guided by admirals who actually understand what it's like out there.
This is a good position for an older sim ... but part of your heart will always be out there in the black.
10. Commander in Chief, Starfleet M,T,W,R,F 10 am - 3 pm §500/hour
You're in charge of the whole thing; the buck really does stop here. You set the direction for hundreds of ships and thousands of people, using all of your experience and wisdom to make Starfleet's future ever better and brighter. Go ahead, implement your vision!
SCIENCE AND SHIP'S SERVICES Track:
5. Communications Officer M,T,W,R,F 8 am - 2 pm §60/hour
You serve on the bridge now! This is where the action is.
Incoming orders from Starfleet, outgoing reports from the captain, negotiations with alien ships, greetings to new planets, calls for help from landing parties ... it all goes through you.
Open those hailing frequencies and listen hard!
6. Computer Specialist M,T,W,R,F 8 am - 2 pm §70/hour
The computer controls the ship – everything from the helm to phasers to life support is computerized – so this is a key job. Do it well, and the captain and first officer will notice. Work on your logic and science skills if you'd like a position with more variety.
7. Astrophysicist M,T,W,R,F 8 am - 2 pm §85/hour
From star mapping to the analysis of nebulae, your job is to study the stellar objects all around you. You'll be expected to help the ship steer clear of black holes ... except when the captain wants to go back in time and has to slingshot around one for energy.
The rest of the crew may LOOK at stars, but you get to KNOW them.
8. Science Officer M,T,W,R,F 8 am - 3 pm §100/hour
You have information on every possible subject at your fingertips, the better to inform and advise the captain. You also manage all of the specialist scientists under your command, since as a generalist, only you have the knowledge to see how all those specialties fit together.
This may be the most intellectually satisfying job in Starfleet, except possibly for Head of Starfleet Research.
9. Instructor at Starfleet Academy M,T,W,R,F 7 am - 1 pm §200/hour
Science officer was a fun job, but it WAS a bit strenuous. As you age, it becomes your responsibility – and your privilege – to train the next generation of Starfleet officers.
It's hard to believe that you were ever this young and naive, but the next cohort of Starfleet officers comes from the kids you're teaching now!
10. Head of Starfleet Research M,T,W,R,F 10 am - 3 pm §400/hour
You know more about Science and Advanced Tech than anyone, which means you know where the gaps are. This makes you ideally suited to determine the overall research direction of every starship in the fleet AND to direct the groundside tech development that produces new and upgraded equipment for the people out there in the black.
You direct thousands of scientists on hundreds of ships and worlds; the future of Science herself is in your hands.
BRANCHES
This career is designed to let you grow up to be Kirk or Spock, and even to go beyond them, into job levels that are more appropriate for older sims (because you probably don't want to be getting into fist fights when you're 70. :-D) There's no way to grow up to be Scotty or McCoy, because their jobs require the specialized training of an entire track apiece, so including them would require FOUR career branches ... and the game engine doesn't allow that. :-)
If you decide to go for the Science and Ship's Services Track, you'll need the University Life and Ambitions expansion packs, in addition to Into the Future, because that track uses the Science skill that came with University Life EP and the Inventing skill that came with the Ambitions EP. (Spock knows how to do almost everything there is, so if you're going to grow up to be him, you'll have to learn a heck of a lot. But there are opportunities and events to help you!)
Please do NOT try to take the Science track if you don't have the necessary EP's, since that will mess up your sim's skill list! The Command track uses only base game and Into the Future skills, so you can still play the career even if you don't have Ambitions and University Life.
It wouldn't all fit in one message, so more in the next one!