To add to the exiting writeups, is one of the earlier web-based communities on the net. It was founded in 1995 by MIT computer science professor Philip Greenspun. He later used as the basis for a consulting company he founded, ArsDigita, which implements similiar community systems for about $750,000 a pop. The basic software development kit of, known as ACS (a tcl/tk layer running on netscape server with an oracle db) is now open source, so you can roll your own for a lot less money.