What are the open source alternatives for Facebook? [closed]

Question

Just want to look at how things are implemented for learning purpose and may even contribute something along the way. So is there any open source facebook clones out there ?

Thanks

Answer 1

Searching gives

1. Diaspora
2. OneSocialWeb

as starting points, a list of active distributed social media sites can be found here

Answer 2

This one is most polished right now: http://elgg.org/