while you are at it, you might want to look at
phpGroupWare
I have not looked at it in a while, but did seem to have great potential. Their idea is not too dissimilar to openACS, with a core, seperate modules, and strong permissioning. They also have a decent online demo.
There are a few more groupware projects at www.hotscripts.com.
Might have time in the next couple of weeks or so to do a comparison of features between these and openACS. While some of these projects are not enterprise class, I feel there are lessons to be learnt, especially on the UI front.
