Groove mainly brings offline support, synchronisation and security on top of .NET. Which is a funny story since replication is one of the few points where Lotus Notes outshines its competition.

05/21/04 update: Adesso "is a rapid-development platform for building, deploying and managing mobile applications for the enterprise, workgroups or mobile professionals. Adesso applications reside simultaneously on Pocket PC's, Tablet PC's, laptop or desktop computers as well as one or more servers."