Julian Bond came up with a means of grouping social software into four core categories. The services in each quadrant are by no means exhaustive. However, I've found it helps to explain the different social media phenomena and how they relate to solving problems in the business world.
SwarmTeams is a special case as it enables people to form groups using techniques that mimic the biological & social dynamics of swarm intelligence. The BBC has recently aired an amazing two part documentary, Swarm: Nature's incredible invasions. The second film, One Million Heads, One Beautiful Mind visually captures and expertly describes how collective intelligence has made insects the most sucessful species on the planet, but fails to ask the question: what if human beings could self-organise this way? How useful is that to organisations today?