To be fair, it is a FTP with permissions and a decent user interface, and plays nice with a Microsoft ecosystem.
Whether that is worth what Microsoft is selling Sharepoint for, well, that depends on the buyer. It also has the "nobody was fired for buying IBM" point (and Microsoft does have decent support).
I still haven't seen an Open Source Sharepoint "killer", though I might not know of it (I had good hopes for Alfresco).
What do we need Excel for when we have perfectly good Perl and CSV files, you might as well ask...