Does SharePoint have any competition?

Stay tuned... I'm going to jump into dangerous territory... does SharePoint 2007 have any competition, and what are the trade-offs?

To give you a preview, SharePoint occupies a new niche in the ecology of computing systems and standards.  There are a number of other entries into this same niche, but the niche is so new that it is still taking shape.

It is a big topic, but I'm going to discuss the more obvious attempts to define and dominate this new market niche.

Comments, as always, are welcome.