I'm not a big fan of mixing fantasy and sci-fi in gaming. I see them as two very distinctive genres and typically I want to be immersed in either one of the other during play. But a little while ago I had a subscription to Paizo's adventure paths and got the "Iron Gods" one, which is an extended homage to the old D&D module "Expedition to the Barrier Peaks". I got it just to see how they'd do an entire campaign of mixed fantasy and sci-fi. Overall I liked it but still wasn't sure I'd want to run that type of game. Paizo has a couple companion products out to support it. I've had them on wish list, but as lower priorities. Then yesterday Paizo put out their "rainy day" sale for 10% off and I decided to take the plunge, buying their "Pathfinder Player Companion - People of the Stars" and the "Technology Guide".
"People of the Stars" is only 38 pages, cover to cover, but it does what it says. You get four full player races, a couple less detailed races, a good selection of thematic traits and archetypes, sidebars on each of the planets in the solar system for Paizo's campaign universe (properly detailed in their "Distant Worlds" book, which I recommend if the topic interests you), some magic items, and brief rules on gravity, vacuum, and other planetary/space conditions. There is tantalizing mention of the Dark Tapestry, an evil alien interstellar conspiracy, but you'll need one of the Iron Gods books for details on that.
I liked two of the races (android and kasathas) but wasn't exited by the other two--but that's just a personal thing. The other bits were only okay I thought. So overall I was mildly disappointed but don't feel I wasted my cash. I'm considering how to run a campaign set in the D&D ethereal plane, which is similar to a interstellar setting, and this book is good food for thought towards that end.