In OpenACS there is a set of functionality in a package called the ACS Content Repository which encapsulates a core API for managing content (text, images, whatever) and revisions thereof. Any content-based ACS packages that use the CR (content repositary) have easy access to things like indexing, hierarchical storage management, etc.
The OpenACS CMS package makes heavy use of the CR package, but so do packages like lars-blogger and bug-tracker.
How that relates to what other projects call a "content repository" may or not be interesting.
