I'd not heard of open source EpiCollect developed at Imperial College London:
EpiCollect is a generic data collection tool that allows you to collect and submit geotagged data forms (along with photos) to a central project website (hosted using Googles AppEngine) from suitable mobile phones (Android or iPhone). For example, questionnaires, surveys etc. All data synchronised (ie a copy sent from the phone) from multiple phones can then be viewed / charted / filtered at the project website using Google Maps / Earth or downloaded.
Furthermore, data can be requested and viewed/filtered from the project website directly on your phone using Google Maps.
"While we have had CMap around for a long time, this new version really shows what our team of programmers can do with Open Source technologies,” said Dave Cummings, Clackamas County Chief Information Officer. “Using Open Source really provided the county some significant cost savings.”