I just had a look at the online demo for Kubi Client, a collaboration tool that's embeddable in Outlook in Notes and offers some of Groove's features without requiring any additional infrastructure. It seems a nice idea to rely on SMTP only, although I always hate to even look at software from companies that make statements like this:

The company"s patent-pending protocol is SMTP-based, enabling it to cross firewalls and leverage the worldwide messaging network, and XML-formatted, to unify the differences between competing Email platforms.

How can the idea of sending XML over SMTP possibly be worth a patent?
Anyway, since this is something unavoidable with US based companies, I'll take a look at it anyway.