[Explain.]
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 ]