As I have said countless times, sourcebooks are a great resource for DMs/GMs to help expand their own games, regardless of originally what system they might have been created for. Of course, if you want to use the book with a particular system, or if you like a particular system and have been clamoring for more books for it, there's nothing wrong with that, either. Up on Kickstarter now is the Gossamer Worlds Compendium, a sourcebook for the Lords of Gossamer and Shadow diceless RPG (because sometimes you want an outcome to be definite and not left to the whims of chance).
If nothing else, it's a book that has a world where you can ride a t-rex with power arms. I want to ride a t-rex with power arms (but then again, who doesn't?). There's also worlds in only two dimensions and worlds that are complete nonsense. There's over 250 pages of material to add to your game.
The campaign is well and beyond their funding goal. So it's stretch goals for the next 29 days.