Intro from http://wiki.openstreetmap.org/:
OpenStreetMap (OSM) is a project aimed squarely at creating and providing free geographic data such as street maps to anyone who wants them. The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive or unexpected ways.
OpenStreetMap and OSGeo
OpenStreetMap is a highly regionalized effort and information is available in English, Czech, Deutsch, Italiano, Español, Nederlands, Slovak, Slovenščina and Svenska (check the Wiki for current status). OpenStreetMap bridges the gap between software and geodata that is inherent to most other implementations. Both tie in perfectly with OSGeo's mission and add considerable momentum to the Public Geospatial Data Project.
One of the caveats of OSM results from bridging the gap between software and data. It has to be paid for with reduced interoperability to standardized software, which in part is also responsible for scalability issues and inconsistent semantics. OSGeo's comunity should have the potential and the means to help resolve some of these.
OSGeo Local Chapter D-A-CH
The German language local chapter of OSGeo is represented by the FOSSGIS e.V. The German language OpenSteetMap community uses the FOSSGIS e.V. as a means to handle transactions, organize rental of GPS devices, organize booths at conferences, print and distribute marketing material, etc.