Hello Scroundrel,
Welcome to the boards and Traveller Universe. Yes the T20 Handbook, THB, is basically the first 8 books from the original, called Classic, Traveller (CT). CT has evolved over a 25-year period and has a large amount of material covering at least 3 different or alternate periods. Here is a quick list.
CT: 8 core books setting up the basics of character generation, starship construction - primarily merchant vessels, world/adventure creation, ground/planetary military characters, naval starship/naval & marine characters, stellar systems, trade, and robots. In the Original Traveller Universe (OTU) the Third Imperium (3I) has brought back interstellar commerce after the collapse of 2 previous Empires and the Long Night. Adventures and magazines developed the OTU. Most of these are available from various sources.
MegaTraveller (MT): An attempt to alter the course of the Original Traveller Universe (OTU). Here the Third Imperium (3I) has splintered into factions and is fighting a civil war.
Traveller The New Era (TNE): The MT timeline ended in a stalemate without any of the factions being able to get the upper hand. At some point between the piont where CT and MT diverged a starship crashed on a planet with silicon based life forms that ate the computer chips. These creatures absorbed the programming and when the planet was rediscovered were found to be useful in the construction of computer cores. Of course researchers figured out how to create a virus using these living chips. At some point in the MT Civil War someone released the Virus, which rapidly evolved and caused the collapse of the majority of the 3I causing another Long Night. TNE is the rebuilding of interstellar trade.
Traveller 2300 AD: This is an off shoot of Traveller and the game "Twilight 2300 AD" IIRC. Instead of an alien empire, Terrans have reached the stars. Of course we've encounter other starfaring beings. There are still the rivalries between various political groups from Terra and at least one of the alien groups. This may not be considered a part of Traveller, but there is a following.
Marc Miller's Traveller (T4) as far as I can tell is another attempt at changing the MT timeline.
GURPS:Traveller (GT) is an alternate timeline starting at the point of the assassination plot in MT. The assassin is killed instead of Emperor Strephon and family.
T20 condenses and converts the CT core books into the d20 system in one book. I think there are some adventure listed here in the elibrary. Here is a link to a site that may help you find out more about the Traveller background:
Open Directory
Hopefully the link keeps working and since this is my fourth attempt to post a reply I am going to quit and post now.
Originally posted by Scoundrel:
I've recently gotten T20 and am impressed with how the D20 rules have been adopted for science fiction. I'm also a newbie to Traveller as a whole, and as a result, I'm rather confused. every Traveller fan I've talked to has talked about the great neo-roman hard SF setting, but in the T20 book, I get a smattering os species and vehicle descriptions, but no setting.
Some help, please?