Forum OpenACS Q&A: Re: Evaluating OpenACS
OpenACS has all the infrastructure to support the scenarios you have in mind. The plumbing is all there, so to speak. However, the applications are in different degrees of readiness. A number of .LRN (dotLRN) sites use ETP (Edit this Page) for content management of HTML pages. You can couple this with the OpenACS blog to post News etc. as well.
OpenACS really shines with how it handles permissions and categorization. The best way to get familiar is to download it and start doing a test drive.