More and more projects are becoming available to replace the Flash Media Server, surely a sign of the success of this technology. This is an incomplete list. I hope to be able to add some reviews at some point. Most are focused on one-way video streaming and lag collaboration features although Red5 and Wowza offer at least basic collaboration possibilities.
Open Source
Red5 - http://www.osflash.org/red5
Haxe - http://code.google.com/p/haxevideo/source
Commercial
Wowza - www.wowzamedia.com
Onlinelib - http://www.onlinelib.de/
Sevenload - http://www.sevenload.de/
PHP solutions
http://www.flashcomguru.com/index.cfm/2005/11/2/Streaming-flv-video-via-PHP-take-two
http://www.rich-media-project.com/