Microsoft has a lot of enterprise applications out there. Is SharePoint their leading product in terms of collaboration?
Well that depends on what you mean by collaboration.
If you want to collaborate by sharing data stored in documents or list then Yes SharePoint is your product.
If you want to collaborate on creating documents with simultaneous editing then Office Web Apps is your product.
If you want to collaborate by sharing knowledge in the form of discussions, then Yammer is your product.
If you want to collaborate using e-mail then outlook/exchange is your product.
All of this is combined in Office 365, so that's probably what should be called the leading Microsoft collaboration "product".