Mobilizon - A free and federated tool to get our events off Facebook
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Mixily - Hosting your event just got easier.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.
Facebook Local - Discover places to go and events happening near you
Get Together - Get Together is an open source event manager for local communities.