Joel on Software has an article on Building Communities with Software

The article discusses some of the community software currently available and the effect these different implementations have on the community that's formed. USENET, Slashdot, and IRC each have specific issues that characterize their interactions.

Joel's primary axiom of online communities?

Small software implementation details result in big differences in the way the community develops, behaves, and feels.

For example:

IRC users organize themselves around bot warfare because the software doesn't let you reserve a channel. Usenet threads are massively redundant because the original Usenet reader, "rn," designed for 300 baud modems, never shows you old posts, only new ones, so if you want to nitpick about something someone said, you had to quote them or your nitpick won't make sense.

He then goes on to discuss what he has found that does work, what doesn't work as well and why.

Sometimes in communities it's not so much a matter of what works or doesn't (which Joel also mentions) but what kind of community you want and what's the best way to get it. It's often a question of matching up the community with the software and going forward from there.