Grouply - manage all the groups you belong to in one spot by getting all your emails in a digest, also has social networking (what doesn’t)…reminds of Fuser.
Also checkout Linqia, this is a place that has aggregated groups across the web so you can browse them in one spot…listen to a great podcast.
Profy - an RSS Reader, blogging platform, and social network (send IM, msgs, add friends) in one, also see Buddypress.
I still like the idea for a distributed social network for the blogosphere.
CoveritLive - live blogging in that as you blog it’s being streamed (no need for a submit button), perhaps this is text streaming. Visitors can interact, take part in polls…what a great idea for events.
Feedhub - upload your OPML and it’s claims it will learns your preferences and delivers items that you really want to see…it generates a feed so you can read these items in your RSS Reader. AideRSS does this sort of thing based on social popularity rather than personal…Particls is the most advanced tool in this space.