The Open Architecture Community System (OpenACS) is a Web development framework for building applications that support online communities.

OpenACS provides a robust infrastructure, building on top of the following standard components: the TCL, a [ Postgresql ] or Oracle database for storing the application data, AOLserver for HTTP service and *nix or Windows operating systems.

Like other modern Web frameworks, OpenACS supports: templating for separating the logic from the presentation, internationalization to present the user interface in the user’s preferred language, a modular package system to create sub-applications, a role and
permissioning system, a content repository to store all manner of content and maintain versioning .

Further information, downloads and great community support can be found the OpenACS Home