Both Alternity Player's Book and Gamemaster's Book are great - except I don't like the system itself. Great ideas, tho. As well as the Starships (mostly if you like to tinker with the Traveller Starship paradigm), Dataware (for Computers and Robots), and Mindwalking (if you like Psionics) books. The Alternity Star*Drive Campaign setting is also included with the d20 Future system - if you like d20. But I haven't found a conversion yet. The Star*Drive campaign itself was unique. Interesting, but a little boring. All in all, a good line, but flawed by its cumbersome dice system. Think along the lines of GURPS Space - more of a build your own campaign with the Alternity line. I hear Dark*Matter was good, tho.
Dameon