Uses the AOLServer web server with embedded TCL 8.2 interpreter: Multihreaded, automatically caches interpreted code for speed. Has builtin, easy to use hooks to connect to databases like Oracle, Sybase, PostgreSQL.
OpenACS is a web toolkit built on top of AOLServer. It has a strong community-oriented focus, with emphasis on bulletin boards (aka message forums), news, classifieds, as well as ecommerce functionality. It has a very strong templating system as well.
Users: greenpeace.org[L1 ], openacs.org[L2 ], www.travelerstales.com (most functionality hidden in admin pages)[L3 ], www.pps.org [L4 ] . Probably the most popular and most customized site is photo.net [L5 ]
The precursor to OpenACS is ACS, the arsDigita Community System. There we have the connection to Phillip Greenspun, the operator of photo.net, and author of two books about database backed websites in which he uses the beginnings of ACS as his examples.