Glympse - Glympse is the easy way to safely share your location in realtime. No sign-up needed.
Prey - Prey is the simplest and most reliable solution for tracking, data protection & management for Windows, Mac, and mobile devices. Track with precise location, wipe, reset and secure devices across all platforms.
Zenly - Zenly is a GPS tracker to locate your friends in realtime.
Android Lost - Remotely control your Android phone from the internet or by SMS. Features:
OwnTracks - Cross-platform location sharing
iLostFinder - iLostFinder is an anti-theft/lost app for iPhone and iPad.