Traveller as originally designed was a sandbox RPG without a setting. There was a nascent implied setting via the social scores, having a Navy and Army, and the jump technology was also a setting boundry. But other than the jump issue and lack of interstellar communication outside of jumping starships, it was set up so you could create any setting you want.
Of course, as the supplements built up, the OTU was born and fleshed out until it was pretty securely bolted on to the rules. Now when one thinks of Traveller, one thinks of the Imperium and the OTU. This is a really rich universe with a LOT of supporting material and resources (hello TravellerMap, and hello Traveller Wiki!)
However, as someone who collects a lot of technical manuals for things that do not exist, there are SF resources to play Traveller in other settings. Some I think work almost as-is, while others I just can't see using the Traveller rules to play.
So, in no particular order, here are my ideas. I'll also add in a completely subjective range of 1 = really won't work well to 5, perfect fit. A lot, if not all, of these have their own dedicated game systems, and usually those are tailor-fit to that specific universe. And I'll also note that the GURPS Traveller rules, and GURPS in general, is designed specifically to be generic. I've never played nor run a GURPS game (though I really love the supplements for Traveller and have several in print). But it was designed to handle any and everything.
In the admittedly limited amount of IP games I've played or run, I will note that trying to run a game like a TV episode has far too much rail-roading to be an enjoyable experience. TV shows have writers with a plot they want to cover in a designated time. They also have the ability to write character actions to further that plot. As we all know, GM plans rarely survive the meeting of the players and things go sideways right off the bat. Using an episode as the nucleus of a game is great: you have all the set pieces, even if they don't all get used. But do not try to recreate an episode as it appeared on TV.
And finally: anything can be run using pretty much any rule set. What really matters is that both the referee and players are having fun. I've played games that I did not think would be fun and they were a blast because of the group playing. With the right GM and players, anything can be played with pretty much any game system. The entirely subjective scores below would be 5/5 if the right group were playing honestly. But it would be bending or breaking the Traveller rules. Some will require a LOT of house rules. But as we all know, like all RPGs, Traveller is simply a framework for a shared game of make-believe to have internal consistency.
Star Trek
Definitely a big ship universe, Star Trek has always been one of my favorite shows. There are a huge number of resources for this as well (as witness the many technical manuals and ship books I have. What can I say but repeat that I really like spaceships!) But for Traveller rules, I don't think you could do justice to the Star Trek universe. Transporters are available at TL 17 I think, and the warp drive is a far cry from jump drives. There is also the issue of interstellar communication: the original series had far more limits on it than later series, but even the later series had some limitations. But near-instantaneous interstellar communication existed, nonetheless. With TL 17 come a host of other things that, while at least with T5 there may be rules on, Classic Traveller would have a hard time to deal with. I have played a Star Trek game, and it was a lot of fun using the d20 mechanics. However - earlier eras for Trek would work fairly well. The Enterprise series did not use the transporter a lot to begin with. And there were several episodes across multiple series that could be readily adapted to a Traveller game. It is definitely a big ship universe though. Career-wise, Navy would work for Starfleet, and the science career would be used if playing on a Starfleet ship. However - there are so many other possibilities beyond just Starfleet: colony worlds, Marquis style of guerilla warfare, even merchants which are used a bit in various series. Using Traveller rules, I give this a 2/5 to play, maybe higher if you forego playing a Starfleet character and just play in the fringes of that universe.
Star Wars
Another big ship universe, it is also a small ship universe what with the Millennial Falcon and other freighters (though there really is not a lot of cargo space in that ship). I believe way back when Classic came out, more than one person worked up the light saber as a weapon (hey, what are rules for except to help you make your stuff up?) Though these ships apparently never needed fueling so the ship technology is far different, including fighter craft that can go to other systems. Then of course there is the whole Jedi thing. Psionics can cover that really, though I've never been a fan of psionics in Traveller, even as weak as it is. I think Star Wars would be a better and easier fit, but there are some great RPGs out there already for it that fit much better. Outside of the Jedi and sub-100-ton ships having some sort of jump drive, though, there are lots of worlds that seem could be easily played in the Traveller rules. Worlds that are basically
planet of hat worlds. Yet worlds with generally a lower TL than available in the "core" worlds. Funny how that keeps showing up in science fiction, though I suppose it may well be how things work out assuming we ever get to other planets. You even have the big, bad Imperium, defined social ranks, and areas far out of its control. Using Traveller rules, I give this a 3/5 to play by using Traveller rules.
Space:1999
Another of my favorite shows, this is definitely a small ship universe. Other than the moon making apparent jumps through space, this show is a really good fit, I think. Limit the TL to 9 or so, and this show could be an exciting thing to play with the planet of the week somehow. I have the
Moonbase Technical manual and it is a great resource. I think you could play in this universe with no changes to the rules at all, just some additional technical things. I think the careers would work as-is, though the Navy would probably be the Eagle pilots rather than an actual Navy. Fun thing: I never noticed when I originally watched the show way back when the stuff about the gravity generators. Think that comes into Traveller either at TL 8 in the Classic, or perhaps TL 9 in some of the newer versions of Traveller. I even have some deck plans that are pretty close to an Eagle, though you could just use the 50-ton modular cutter as it is essentially the same (and probably based on the Eagle). It could even be part of an MTU based off the OTU: a wandering moon that somehow hits jump space randomly (though this is Grandfather tech). This IP I give a 5/5 for being able to use the rules.
UFO
A precursor really to Space:1999, this is another series that I really like. And really hoping they end up making a technical manual for as well! This is another universe that is small ship, and even a lower TL limit than Space:1999 with some exceptions. They do have a moon base that has gravity, but their ships are reaction-based ships. They just have regular weapons, so this is a TL8 game. The main thing are the UFOs themselves: these are visitors with a much higher tech level. UFO could be played pretty much as-is without any rule modifications needed either. It could be played as an invasion type of game with players based on the moon base, SkyDiver or HQ. It would be fun to drive one of those Mobiles around! I had a Dinky toy of one as well as the Interceptor. Wish I still had them! I think there us a lot of potential to play in this universe, even within the OTU. Find a TL 8 or 9 planet with a balkanized government code, make it not part of the Imperium and have a neighboring, higher-tech world needing the biology of this world for some reason. This is also a 5/5 to play within the rules as is.
Aliens
The whole Aliens universe is pretty cool, and I do have a couple of really nice technical manuals. The Hostile RPG, which I think is a Cepheus setting, handles Aliens really well. The Traveller rules would not be broken, though ship travel is a bit different. But the other base limitations of the rules fit well within this universe as well. Most of the career paths can be used as-is, and the TL max is probably 10 or so. Pretty sure this could be played without any real changes to the rules as well, other than interstellar travel. Throw in Striker to make some of the weapons needed, and you could play in the Alien universe pretty easily. To play it right you would need to have the xenomorphs defined, and yes, someone did do that years ago somewhere, with the serial number filed off. 5/5 for using the rules as is to play.
Dan Dare
I have this interesting Haynes manual for
Dan Dare. This is a very pulpy comic from way back in the 50s I believe. They have interplanetary travel, several alien races, and some interesting technology. Probably a TL limit of 9, with some exceptions. It would be an exciting universe (okay, exciting system!) to play in. Some of the alien races have much higher technology, but I like the idea of beings from Venus and other planets, and of course, there is a greater interstellar community. There are a lot of adventure possibilities just from the technical book, though I'd have to read the comics to get a better feel in this small-ship universe. There is nothing from what I've read in this book that has any serious issues with the Traveller rules, so it would be easy to play. Heck - I would not be surprised if this belongs in Traveller's Appendix N. 5/5 again.
Battlestar Galactica
I love the old series, as flawed as it is. Galactica 80, well, we can choose to pretend it never happened (Glen Larson wrote it primarily for his grandchildren was one story I've heard). The new series I did not manage to finish. While I enjoyed the updated effects, it was too depressing for me. Here they are, the last remnants of the colonies, and all they do is fight amongst themselves. Probably a realistic appraisal of the human condition, which is what I think I found depressing. Anyway - the jump is a lot different, but other than that, the technology all fits well within Traveller. TL is maybe a 10, perhaps an 11 in places. Navy is of course the Viper pilots and crew of the battlestar. All the other careers obviously exist, just as survivors on various ships. This would have a lot of potential I think as well and could be played in a number of ways. The other big change would be the ship combat: I don't think Traveller handles the dog-fighting that you would want to play in a Galactica game. I'd give this a 4/5 for playing with Traveller as I think we'd need to graft in some good space dog-fighting rules from somewhere.
Six Million Dollar Man / Bionic Woman
Well, cyborgs such as Colonel Steve Austin and Jamie Summers are a pretty high TL and not really covered in the original Classic rules. Cyborgs are covered in later editions and supplements and things. I will admit that when I played in college back in the 80s, my Scout character did almost die and got bionic legs. We just did what all gamers do and use the rule of cool rather than any specific rules or mechanics. I even threw in a bit of Robocop as he did have a small gun in one of the legs. This would be a TL-7 game with the exception of robotics and cyborgs which are probably TL 10 or 11, or even higher depending on the rule set. At this point, though, it is more a superhero game than a Traveller SF game. While the rules would work, I think to really enjoy playing in this universe a more bespoke ruleset may be a better choice to handle the more TV episode style of play. A 3/5 as yes, it is a pretty good match rule-wise, I just don't think it would be in actually using the rules.
Visitors
I never watched the remake, and just have vague recollections of the original series (I do recall I really liked the shuttle craft). This is something similar to UFO: TL-7 humans against TL-A or so aliens who are more alien than we expect. Can Traveller rules play well here? Certainly. Would it be fun? Under the right referee I think it could be a blast. I am just unsure if you could get a lot of mileage from it. I'll give this a 3/5 as well, simply because while the rules can easily support it, as with the Six Million Dollar Man I don't think Traveller rules could encompass the feel of that universe.
Firefly
Well, most people believe this was based off a college Traveller game to begin with, so obviously this is an easy fit. Biggest thing is to remove the jump drive: Firefly existed in a single system that had several terraformed worlds. Maneuver all the way. Technology goes a bit all over the place here, though probably 11 or 12 would be the max for most places. The inner system obviously a higher TL than the outer planets. And dang - now I want to watch that series again. May have to buy the DVDs or something. I did rent it years ago from Netflix I think, so I managed to watch it in the correct (if far too short!) order. This is a 5/5 to play with the Traveller rules, just no jump drive.
There are plenty of other shows that may be an inspiration for Traveller games. I'd really like to try a Space:1999 game, or a UFO game and may try that some time with my group. And I think I could run a Battlestar Galactica game if I could find some good dog-fighting rules that my group would like.