Glympse - Glympse is the easy way to safely share your location in realtime. No sign-up needed.
Pleroma - Pleroma is a free, federated social networking server built on open protocols.
Zenly - Zenly is a GPS tracker to locate your friends in realtime.
GNU social - GNU social is communication software for both public and private communications.
LockOnMe - LockOnMe is a location-sharing app, displaying targets and associated Points Of Interest on maps & fun radars.
ZeroMe - Social network for the distributed P2P network ZeroNet.