Just to correct something that Peter said - OpenACS has been listed on
dmoz.org since April 2001 in
Computers/Software/Internet/Servers/Discussion (along with phorum.org and slash). Dmoz.org is the basis for Google's directory (an example of the connection is that currently every dmoz.org page has a green ball in the bottom right that links to the equivalent category on Google). OpenACS is also listed in
Computers/Software/Databases/Oracle/Tools/ (since Feb 2002). I originally submitted OpenACS for inclusion in Dec 2000 - I am ODP editor, I originally joined to see a large scale community site in action.