Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Glympse - Glympse is the easy way to safely share your location in realtime. No sign-up needed.
Event Hunt - Startups and Tech Events Curated By Locals
OwnTracks - Cross-platform location sharing
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Zenly - Zenly is a GPS tracker to locate your friends in realtime.