This is a non-definitive list of all the active discussion lists around the OSGeo projects.
Collabnet uses ezmlm for mailing list management, so if you know a list address, then to subscribe to it, email [listname]-subscribe@[project_subdomain].osgeo.org
Main discuss list
Incubation Committee list
Visibility committee list
Web committee discuss list
email@example.com (List archives on CN)
firstname.lastname@example.org (List archives on CN)
Mapguide users list
email@example.com (List archives on CN)
Unused lists / groups?
These projects all have the default collabnet list setups, and none of them seem to have traffic.
Conference organising lists - they are the collabnet defaults, and none of them seem to have traffic.
FDO dev list - this only has the dev list, not the other defaults