The T20 system combines the class and level character aspects of the d20 game engine with the tropes and many of the mechanics common to the various traveller system games, including prior history generation, High Guard compatible ship design, Traveller worlds, Travel, and Trade. Characters will generally start between 2nd and 8th levels.
From the back cover:
Traveller20 (T20) combines the Popular d20 game mechanics with the most fully realized science-fiction game setting ever - Marc Miller's award-winning Traveller.
Presented in a single volume, these rules allow you to go anywhere, do anything...