MegaTraveller (MT) was the second incarnation of the Traveller role-playing game published by now defunct Game Designer`s Workshop (GDW), which combined most of the rules of the Classical Traveller (CT) days, and mostly improved on them. One of the greatest achivements of this ruleset was the integration of a task system into Traveller, as well as creating an integrated rules set. However, a lot of typos and missing tables occured during the writing thus requiring a lot of Errata afterwards, which also let to MT to be called "The Errata Edition".
It was mostly written by the crew of now defunct Digest Group Publications (DGP), as the GDW staff concentrated on other projects such as Twilight 2000.
The greatest change MT brought however, was the Rebellion in the Third Imperium, which started when Archduke Dulinor if Iliesh shot Emperor Strephon Aella Alkhalikoi, as well as his wife and daughter, dead, but failed to take the throne for himself, thus shattering the Third Imperium, when no clear line of succession presented itself. Various factions arose to battle for the Iridium Throne, and the enemies of the Imperium such as the Solomani and Vargr exploited this weakness.
The MegaTraveller background is part of Traveller canon.
There were three main rulebooks and various sourcebooks in MegaTraveller:
Player Handbook, Referee`s Manual, Imperial Encyclopedia (being the core rule books), Referee`s Sourcebook (which contained more information on the Rebellion, COACC (Close Orbit Air Command), Fighting Ships of the Shattered Imperium (a collection of warships) and Hard Times (details on the collapse of entire worlds when the factions trenched themselves in and left entire subsectors without support).
There were also a couple of adventures published. First and foremost "Knightfall" and "Arrival Vengeance", and some more set in the Hard Times Era. Other information was published in GDW`s house magazine Challenge.
Additional to the GDW effort, there were supplemental releases by other companies, most notably DGP and Seeker. While the first published excellent information on alien races and factions (Vilani and Vargr, Solomani and Aslan, campaigns (Flaming Eye), rule sets (World Builders Handbook, Starship Operators Manual), play Aids and magazines ([first Traveller's Digest, later MegaTraveller Journal), the latter concentrated entirely on providing starship deckplans for a great variety of Traveller spaceships.
There also was a Japanese edition of MegaTraveller, which suffered from the same errata problem.
The Traveller RPG was originally developed by Marc W. Miller and Loren K. Wiseman. Today, Marc republished collected editions of Classic Traveller, while Loren works as line editor for the GURPS Traveller line at Steve Jackson Games.