I'm looking for an open source projects, code-a-thons, or organizations which create software used for charity purposes or to help out charities. There must be a demand, but it is hard to locate them due to the wide variety of terms used to describe what they do. My preference is for sites with some degree of a positive reputation or some proof of effectiveness, such as through the number of charities helped.
I understand that many of these may be localized, but my hope is to build a list of possible organizations to consider contributing time towards. I think this is on-topic because of "freelancing or business concerns" and it's only a moderately subjective question. GiveCamp is a good example (thanks, ElYusubov!) but We Are Microsoft is not so good since it's stale from 2010.