GURPS: Aliens

 From the website:

"We Are Not Alone

In fact, every time we open the airlock, we meet a new race . . .
GURPS Aliens presents over two dozen new races for your campaign! Use them in any science fiction adventure . . . or fantasy, or horror. Or, if you're tired of throwing the same old metavillains at your GURPS Supers players, these alien allies, foes, and technology will keep your game flying.
Many of these races are suitable for use as player characters or allies . . . some are implacable foes . . . and a few are truly alien. Among the creatures you'll meet:

• The tentacled Purulu, galactic meddlers and misers. These radioactive octopi can buy anything they want . . . except a world of their own.
• The Memer and Saret, tramp steamers of the spaceways. These symbiotic partners rarely eat and don't need air or warmth; their slow, leaky ships are vital to galactic commerce.
• The obsessively curious Irari, long-loved winged bipeds who hire other races to do the boring task of ruling them.
• The callous Verms (short for "vermin") – a hungry hive of mind-controlling crabs, who can devour a human community from within.

Race descriptions include:

• Physical appearance – and special physical abilities and limitations, along with the race's preferred environment.
• Psychology – These aren't just people in bug suits! Some aliens have psychologies that are . . . different. What do they want? What do they love – or fear? How do they think and behave? (Then again, some of the strangest-looking races can be very human . . . )
• Racial ecology – what do they eat? How did they evolve?
• Culture, religion, and politics – how do they behave at home? What (if anything) do they worship? How do they deal with humans and other citizens of the galactic civilization?

Also included are rules for designing new alien races, including racial advantages, disadvantages, and skills. Invent balanced alien designs that will intrigue and challenge your players!"