There is an article about Ushahidi on the ACM-Website. Ushahidi is a remarkable system that was originally used for election monitoring in Kenya.
The system is used to collect, evaluate, visualize and map reports or eyewitness accounts. The central element is a web server. There are mobile apps for different devices, but information can also be gathered via SMS. The system is now being used in disaster relief, as well as “community” projects (in terms of regional communities). More information is available in the Ushahidi wiki and in this presentation by Heather Leson.