Get Together - Get Together is an open source event manager for local communities.

Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

emble - Plan better events with your friends

Guestboard - Lead powerfully-organized group events with Guestboard – a modular event platform that gives groups of 10-1000+ people a central space to coordinate, build excitement, and save money. No more crazy email threads. No more massive group texts.

Raft Calendar - A fun and beautiful calendar for couples and close friends

Kommunity - Explore communities that share your passion with millions of people