To follow up Psion's post on Traveller (and this duplicates a little of it, apologies)
Traveller has been through 5 pre-D20 iterations:
- the original "classic" version from Games Designers Workshop (all of it available in reprint from Far Futures), set in a vast, long lived and stable human galactic empire of over 1100 worlds set 3600 years in the future. The original system had rules based on D6, and included a career/background generation system of which the one in the latest Unearthed Arcana is but a (largely unworkable and to my eye not well playtested) shadow.
- Megatraveller, largely the same as classic but (just about) recodified the original rules, added a much needed task resolution system (much like D20 skills resolution) and moved the milieu into a new period of galactic civil war following the assassination of the emperor. This version was largely developed for GDW by a third party called Digest Group Publications and most of this material has not (to my knowledge) been reprinted, for copyright reasons (the best stuff was actually published by DGP and there is an ongoing impasse about republication of this material, there is a possibility of republication of the - weaker - GDW material).
- The New Era, a new (and in my opinion awful) ruleset, where GDW retook command and which moved the milieu a few hundred years forward into a period of post collapse emergence
- T4 - yet another ruleset, post GDW's own collapse. From Imperium Games, Inc. Set at the dawn of the Imperium.
- GURPS - Steve Jackson Games used some new and original "classic" authors to adapt the Megatraveller period for an alternate timeline where the assassination never happened. SJG have published a lot of material for GURPS traveller but it rewrites alot of the canon stuff, either directly or (through its world generation rules) implicitly, and frankly I'm agin it.
The Quiklink adaptation is fine but thus far lacking in background material from the Traveller Universe itself. In fact there's next to nothing in the core book. But they now have a "domain" published in PDF, where a domain = 4 sectors = lots & lots of worlds ... as a guide you used to be able to spend an evening hand-generating a subsector, and there are 16 subsectors to a sector.
GURPS has re-published information for 2 sectors but they took so many liberties I personally would leave well alone. You can get the original Spinward Marches and Solomani Rim sectors as part of the "classic supplements" sets published by Far Futures. GDW originally operated a landgrab system so that third party publishers such as FASA, Judges Guild, etc could define their own sectors, you can get these on ebay in various places but most were declared non-canon in the Megatraveller period. DGP published a large number of sectors in its Traveller Digest magazine. And you can generate your own sector, system and world data however ... and you can get an excellent and free windows program from
http://www.downport.com/wbd/HEAVEN_&_EARTH.htm which will generate systems and worlds according to any of the pre-D20 systems.
T20 is a good blend of classic and D20 rulesets. My biggest issue with the core Traveller's Handbook is lack of support for 3 of the 6 "major" races which dominate the Imperium background. Included are humans, vargr (uplifted wolves) and aslan (lion-like aliens), but not the very alien hiver (much like Niven's puppeteers), k'kree (militant vegetarian centaurs!) and the reptilian droyne.
I'd summarise by suggesting that Traveller D20 (or T20) is a great place to start, and to get the Classic reprints from Far Futures if you want more. Considering the first shipment of T20 sold out on pre-order at my local game store I'm really surprised that QuikLink aren't doing more to develop and support T20, maybe it could do with sponsorship from a bigger publisher.