Online communities usually sharing a topic or tone or demographic whereby members can communicate socially online with one another.

Grabbit.net

Is the world ready for Grabbit?

Because aggregating all of that information into a single stream could create its own information overload, Grabbit lets users instantly filter their streams in a variety of ways to focus on specific information or people. Grabbit also gives users a powerful set of tools for managing friends, contacts, and groups of friends and other contacts, across a wide variety of social and business networks.