Pleroma - Pleroma is a free, federated social networking server built on open protocols.
Twoo - With the millions of active and interesting people around the world, Twoo is one of the most interesting and practical means for finding the new people across the globe.
GNU social - GNU social is communication software for both public and private communications.
Path Talk - Smart, Private Messaging
ZeroMe - Social network for the distributed P2P network ZeroNet.
Qeep - If you are looking for a dedicated application freely allowing you to meet new people and find interesting friends, then Qeep is an application to whom you must give at least one try.