The uncreatively named Planets setting offers just that: 40 planets across the galaxy for your sci-fi campaign, which you can use in the default "Alliance" universe or pick and choose and plop into you present setting. It is ruleless, so you can use your favorite rules, and the book includes advice on how to work in various common rules elements into the setting. The planet descriptions given are detailed and interesting for the most part, complete with adventure hooks for each. My real problem with this setting is the races: apparently humans evolved on many different planets, and no explanation of how this can be is given. Even more offensve to this reviewer's delicate sensibilties is that the not obviously human races are rehashed fantasy races: minotaurs, satyrs, ogres, lizard men, etc. It's silly, and ruins the usefullness of the setting for me. You could, however, use the planets themselves and populate them with more creative aliens.