Social Networking Open Source: Elgg

I didn't know about that (or maybe I did and forget), but there's an apparently superb (opinion based on screenshots) tool in GPLv2 to create social networks, called Elgg. The tool integrates a high amount of connectivity backends for other social networks apps and is certainly something we'll be looking into in the next weeks, to see what can be done and what high-value services we can offer based on this.