Pro-Sys Community Server

CommunityServer.org - The community for Community Server. The best place to start!
Licensing & Add-ons - Details on licensing and additional features for your Community Server system.
User documentation - Includes how-tos and explanations for Community Server features.
How to Videos - Watch an ever growing list of videos about Community Server.
Support, development, and hosting - Contact Telligent for support, as well as hosting and custom development recommendations.

Other useful resources:
Community Server Announcements Blog - Subscribe and keep up-to-date with the latest announcements.
Community Server Daily News Blog - Subscribe and get daily updates about Community Server.
Software Developer Wiki - Basic developer documentation.