Versions of Traveller
'Traveller' was published in various editions. Some games tied directly into the RPG system, others were more loosely based on systems from the Traveller Universe. Traveller was orginally designed as a science fiction RPG (one of if not the first), and the original setting was just one the designers favoured. While referees were encouraged to use the parts they wanted and change what they did not like, the wealth of background material made the Classic Traveller setting ubiquitous.
Major Versions
Each of the versions of Traveller used a slightly different setting from the traveller universe. Classic Traveller takes place during the Third Imperium, Megatraveller during the Rebellion. The New Era takes place after a computer Virus ended the rebellion period, during a time of exploration/reconstruction. GURPS Traveller takes place in an alternate timeline where events from MegaTraveller and The New Era never occurred. Traveller 4, Traveller 5 and Other versions of Traveller take place in the early days of the Third Imperium. Each system also devised new rule systems to handle playing of the game: while characters can usually move from system to system without much effort, other creations such as ship designs will not, though deck plans (often loosely based on the underlying ship designs) are often used across versions.
Traveller, Classic Traveller or CT
1977-1986 Original Rules. Set in the years 1100-1116 Imperial, around the time of the Fifth Frontier War.
MegaTraveller or MT
1986-1991 Task-based system. Set in the years 1116-1124 Imperial, during the time of the Rebellion.
Traveller: The New Era or TNE
1992-1995 Twilight2000 rules. Set after the year 1200 Imperial, post Virus timeline.
Marc Miller's Traveller aka T4
1996-1998 Set just after Year Zero, in the early days of the Third Imperium.
GURPS Traveller aka GT
1998-2004 GURPS 3rd Edition Rules. Set in the years 1116-1124 Imperial, in an alternate timeline which differs principally in that the Rebellion of 1116 never happened.
Traveller 20 aka T20
2002- D20 Rules. Set around the year 1000 Imperial, about 100 years before Classic Traveller.
GURPS Traveller: Interstellar Wars
2006- GURPS 4th Edition Rules. Set in 2170 A.D., almost 3500 years before CT, in the time of the Nth Interstellar wars.
Traveller: The New Era: 1248
2006- A rules system free update to The New Era, including the founding of the Fourth Imperium.
Traveller5 aka T5
2008 - An updated version of Traveller 4th, published as a CD-ROM/PDF collection. This will mostly be Rules, with little background material.
Traveller Hero aka TH
2006- A version of Traveller using the Hero Games Star Hero rules and covering several previous milieus including Milieu 0, the T20 milieu 1000, and the New Era.
Mongoose Traveller aka MGT
2008- A new set of rules, updating the "classic" Traveller rules. Setting is largely not covered in the core rules book, however supplements will be set in 1105 and centred on the Spinward Marches. The core rules will be available as open content.
Previews of the core rules are now available on the Mongoose Publishing Website, as a downloadable PDF file.
Traveller: 2300 aka 2300 AD aka 2320 AD
Published to be the "State of the Art" science fiction RPG. Uses the same background as GDW's Twilight:2000 game system. The 2nd edition of this game was renamed 2300 AD. The third edition of this game is 2320 AD and requires the Traveller T20 rule set to play.