Not surprisingly, the OpenACS community uses its own software for communication. The main web site at openacs.org is the home to many useful discussions, as well as documentation, software and patches. Indeed, while you can (and should) read the documentation at openacs.org/doc, the discussions at openacs.org/bboard are probably even more important and useful for anyone interested in using this technology.
To install OpenACS, you will also need AOLserver; as indicated in the article, you should use the version at openacs.org, rather than www.aolserver.com. To avoid problems, I suggest that you install PostgreSQL 7.1.3 (and not the more recent version 7.2), available from www.postgresql.org.
Matt's AOLserver distribution is available from uptime.openacs.org/aolserver-openacs/aolserver3.3ad13-oacs1-beta-src.tar.gz.
Detailed instructions for how to install OpenACS, using either PostgreSQL or Oracle, are available at openacs.org/doc/openacs-4/postgres.html. Be sure to read the comments that other users have written at the bottom of the page before following these instructions.