On the Zend Developer Zone David Coallier has a post about an effort starting up in San Francisco called the HackForGood Evening where developers come together to work on software with the sole purpose of helping make the lives of other people better (those who can't do for themselves).
Starting from there we realised that the idea and purpose of writing software to help the lives of the people around us was exactly what we are about but more importantly, this was an idea that should happen more than once. The HackForGood evenings were born. The following day, we decided to put a simple descriptive page together and organised the event on Eventbrite. Once this was in place we plainly announced it on Twitter to see who would be interested. After having received over 30 signups in 2 hours, we knew that we had hit a nerve and decided to make this event a success.
He goes on to talk about the evening - the presentation of the sponsors, the split off of the groups and the work (hours of it) that was done to create things like the winning entry - 911Stealth, a mobile app for contacting local emergency services when you are unable to use your voice.