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.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Facebook Local - Discover places to go and events happening near you