Ask HN: What open source social network software do you use for you community?

I'm currently looking into open source social network software and I'm curious as to what the HN crowd is using. Currently I'm investigating Elgg and Wordpress Mu with BuddyPress.

I'm interested in this because I want to know if there still is a need for custom-made social network software or have the readily available open source software packages taken care of most of the needs of social networks?