Ah, Traveller. The original sci-fi RPG (well, for me anyway - I'm not sure if it was actually the first). It has certainly been the most enduring Sci-fi RPG. As of 2007, it's thirty years old! Quite an achievement.
Over the years it has had its detractors and has seen many changes and much controversy, but still it's there like an old friend that crops up every few years.
The first version is known as Classic Traveller, or CT
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Next, came MegaTraveller, (MT) which introduced a slicker game mechanic and a whole load of controversy with it. The Rebellion and eventually... Virus
Hot on the heels of MT, there came Traveller: The New Era (ignore the Star-Trekish title). This was a game premise I loved; post-apocalyptic Traveller.
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Unfortunately, a little after the game (T:TNE) was published, Game Designer's Workshop went bust.
Not to be deterred by mere details, Marc Miller (one of the creators of the Traveller game) came back with Marc Miller's Traveller (T4). This game moved the timeline back by some 1200 years to the dawning of the Third Imperium... The game as published was filled with misprints and confusing rules. It was short-lived.
Steve Jackson Games published GURPS Traveller (GT), utilising SJG's generic rules. GT chose to ignore the events of the Rebellion and TTNE, continuing the timeline of the original CT.
Traveller Hero (More to follow)
Mongoose Traveller (MongTrav, TM, or less reverently, Riki-Tiki-Travvy [RTT]) is due to be published in the first few months of 2008. (More to follow)
After the publication of the D20 system for D&D and the Open Game LicenseOGL