Just wonder if there is a kind of www.sellaband.com for developers.
Imagine you are running a small web service as your hobby with a bunch of happy users. Now those are asking for a new feature which will take you 400$ to implement based on your hourly rate.
You want to answer: Just go to this site, invest some money in my feature fund; if the 400$ are reached, the feature will be developed, otherwise, your money will be refunded to you.
Just an idea...