BitHub, funds are put into a pool and distributed evenly to anyone who commits. Bithub allows someone to donate to the development, without giving it any direction.
With feedopensource, developers enter into an agreement with a customer, who pays for a short iteration on a feature or fix of their choosing. Feedopensource allows someone to pay for what they want developed.
https://whispersystems.org/blog/bithub/
https://news.ycombinator.com/item?id=6916751