OpenACS is a toolkit for building scalable, community-oriented web applications. It has been in existence since the early 2000's (originally a port of Philip Greenspun's ACS), and runs on AOLserver (or NaviServer, a fork of AOLServer), Oracle and Postgres. TCL, PL/SQL and PL/pgSQL are the main programming languages.
OpenACS is also a open source project (hosted on SourceForge) where ACS stands for "Automatic Configuration Server" also known as CWMP: CPE WAN Management Protocol or TR-069. To be clear, it is related to computer network equipment. This OpenACS uses jboss.
Note: it would be nice to create a CWMP tag to avoid any ambiguity between those 2 definitions.