We do this at Leanpub (http://leanpub.com http://leanpub.com). We're free to use, and pay 90% - 50 cents royalties. Chances are you've seen a few of our books

We do this at Leanpub (http://leanpub.com http://leanpub.com). We're free to use, and pay 90% - 50 cents royalties. Chances are you've seen a few of our books on HN :)