I've run mostly homegrown campaigns, starting with my first, as it began before the OTU was known to me.
Kurgan Dominate: Very first campaign, a mishmash of a variety of SF universes, book, TV and movie included. Major polity was the above named Kurgan Dominate, think Star Wars Empire mixed with Cylons (yes I know, cheesy). The PC's were almost always from one of the smaller human polities at the edges of the empire. Lots of bizarre inventions and weapons, from a variety of sources. Rules set: Classic Traveller, with house rules (additional character types, combat rules, different jump fuel rules). Ran several campaigns in it, including a "Overthrow the Empire!" type campaign that had, at its height, about 15 people playing.
Terran Confederation (1st Ed.): Human only setting, based on extrapolated future at that current time (80's). Major Earth states kept competing out among the stars, until consolidated into Confederation. One polity, lots of frontier, no intelligent aliens. Kept pretty close to standard Traveller tech tree. Rules set: Classic Traveller heavily modified (new combat rules, new weapons, new Book 4 style character generation, new ship design rules, new ship combat system, etc.). Ran three campaigns, one active duty Nave/Marines, crewing a frontier patrol cruiser, one a troubleshooting team, and one a Mission:Impossible style group that ended up being called the "Never Happened Squad".
Terran Confederation (2nd Ed.) Same basic setup as above, but with additional human polities and aliens, including the Aslan, and a anarcho-libertarian human "state" called the Alliance of Free Worlds. Pretty much same tech as above, but with more of an emphasis on computer and commo tech, especially in the core systems. Rules set: GURPS Traveller, and T20. Ran one campaign, again an active duty frontier patrol cruiser crewed with Navy and Marines.
United Worlds: The closest any of my homebrew campaigns has come to the OTU, this campaign has all the races from the OTU and blends them into a different setting, due to different history. Ancients existed, but not Grandfather and his bunch. Vilani "empire" much less harsh, more of a mercantile league, and they amalgamated with the Terrans once they discovered each other. Aslan, and Hiver are part of the UW, and lend their support against enemies like the (more evil) Zhodani, and the K'Kree. Other baddies are the breakaway Terrans known as the Transhumans, or Transies for short. Radical experimenters with genetics, cybernetics, nanotech, and other forbidden sciences, they were thrown out of Terran space before the UW was founded. Tech is much more varied than normal Traveller, with more attention being paid to the biosciences and cyberware than normal Traveller. Rules set: T20, with pieces being taken from a variety of D20 sourcebooks.
As always, YMMV
John Hamill
jwdh71@yahoo.com