Mark Chase's Atomik Alienz...
Now available from Precis Intermedia in its original form.
On par with high-tech gizmos and ray guns, alien creatures are among the dominant features of science-fiction. Since the turn of the century aliens have been everywhere - from Verne's fantastic space adventures to the exotic aliens of Larry Niven. The aliens are already among us, thousands in every bookstore, television channel, and movie theater across the globe. They terrorize our darkest nightmares and stand at the twilight threshold of our wildest dreams. But just as aliens may be fearsome world-conquering monsters, so too can they be wise and benevolent saviors of our own self-destruction.
Atomik Alienz is a generic Add-On which can be used with any game system. This book allows you to create any creature, world, or civilization imaginable, and includes comprehensive information on planetary systems, astrophysics, exobiology, and advanced civilizations based on the research of Carl Sagan, Michio Kaku, Nikolai Kardashev, and many others.
Add-on notes are now included with this product - no other downloads are needed (specific conversions can be found here).
A full review can be found at GameWyrd.