Usually, when new versions of Traveller are published it seems chic to release it in a previously un-explored part of the vast Traveller universe's history. Traveller20 (or also known as T20) was set about one hundred years before the original classic game was set. In it's own vernacular, at the time of the Solomani Rim War around the year 990. The region explored was the Gateway Domain of the Imperium.
There were a few physical books published- the Core Rules, Gateway to Destiny, and a Narrator's Screen, plus a few equipment books and newsletters. Most of the support material appeared in PDF format, but also multi-system supporting various other versions of Traveller, mainly the original Classic Traveller.
There were plans for a d20 version of another Traveller spin-off, Traveller 2320 (the d20 version of Traveller 2300). A PDF was released at one time, but it seems rather difficult to find that now.
While d20 system definitely had it's day on top, the following resentment for various reasons took it to an all time low, in spite of the continued success of Pathfinder. I feel we're coming out of that anti-d20 era. Through it all, Traveller 20 seemed to have had a rather positive respect in fan's opinions. Some still rave about it saying it was perhaps one of the best d20 publications created.
What I recently discovered was that after Quiklink Interactive / RPG Realms lost the license for Traveller, there was a re-release of the products with the Traveller setting stripped out. Similar to what Mongoose did with Legend and RuneQuest. In this process they also cleaned up the products, fixing errata and clarifying some rules, etc. The following series is a solid generic d20 sci-fi game.
This line was to be short lived. The mind behind Traveller 20 and SciFi20 tragicly passed away and the ambition for this line, with him. Hunter Gordon's memory is held high by many Traveller fans.