OpenACS (Open Architecture Community System) is a web application platform 
designed for high traffic community websites. It is built on a free and 
open source foundation. OpenACS is the foundation for many products 
and websites including the .LRN e-learning platform (www.dotlrn.org).

OpenACS runs on AOLserver and uses either the PostgreSQL or Oracle (which is 
not open-source) relational databases. It uses TCL as its main language. 
AOLserver, postgresql and Oracle are used in some of the most demanding, 
high-traffic web applications in the world.

DotLRN (.LRN) is built upon openACS core, but includes extra modules and
configurations. DotLRN has its own tarball and port (openacs-dotlrn).

WWW: http://openacs.org