URL = https://leanpub.com/
"Leanpub is not as good as bandcamp is for music, but it is the closest I have yet to find.
What I like, is that it lets the purchaser set the price, and shows how much is going to the writer.
Leanpub pays 90% royalty to authors, less a 50 cent flat fee.
The writer retains the ownership of their work." (https://keithpp.wordpress.com/2013/08/21/leanpub/)