Open Source Geospatial Foundation (OSGEO) helps to support and build various open source geospatial software. It is the incubator organization for various high profile Opensource Geospatial tools such as UMN Mapserver, MapGuide OpenSource, OpenLayers and GRASS to name a few.
OSGEO also sponsors various Geospatial Events. Upcoming events can be found at the RSS feed below this note.
For open source service providers checkout the OSGEO Open Source GIS Service Provider Directory