In a word, it is a CMS. But being from Microsoft, you know it has to be excessively complicated. So take Drupal, but build it with IIS, ASP.NET, Microsoft SQL Server, XSLT and Search. Make sure you throw in plugins that make it manage Microsoft Office documents very well, with hooks into things like Outlook, and there you have it. It's nice because it has lots of features, but the flip side is it's prone to break down with no way to restore from backup because the restore process is so complicated. It also gets lots and lots of patches every month. Takes up so much memory and CPU that you actually need a farm of them and that's where the complications really start. If you can stick to a single server and small workgroup it's usable. If your company has more than two dozen people in it, you're in for a full-time job to keep the thing working.
I really don't want to mention our product again on the same page, but you mentioned Drupal, which is what we built our, I guess I have to say, Sharepoint alternative: OfficeMedium ( I won't spam another link on the same page )
I think we're on the same page though: Simplicity is key.
Does OfficeMedium have samba sharing or similar feature so documents can be added without uploading via a web interface? I've been looking for a good content management system for my job. Alfresco ( http://www.alfresco.com/ ) seems to present itself as a shared drive on user's PC but it doesn't do events + calendaring that OfficeMedium seems to support.
