Ask HN: How to Transform my Web-App into an Open Source Project?

I have the impression that my web-app (decision making tool http://dezidr.com) might be too small and too specialized to pay the living of its creator one day. I therefore consider to transform it into an Open Source project to make it available to people who like it or to developers who want to extend it even when I move on to other projects and shut down the service.

Does anybody of you have experience with doing that? What are the necessary steps? Is the idea useful at all?