OSGeo is creating many new and old open source tools for geospatial purposes. There are tools for both web-based and desktop mapping. Here is one project - Urban Forest - that has used several OSGeo tools:
"...the project team has created an Urban Forest Map, which digitally pinpoints the location of each tree, maintainstree data in a consistent database, and offers web access to the tree data – key for maintenance and planting efforts. The community can get involved by posting photos and stories about their own trees that they plant and map online. With the launch of this collaborative effort and the support of the Mayor's Office, a critical step has been taken to move San Francisco's urban greening efforts forward...
One of the OSGeo tools from Autodesk is called MapGuide Open Source
