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

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

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

DownToMeet - DownToMeet is a platform to organize, find, and attend group events.

Calendify - Calendify is an event community where you can share, publish, and subscribe to event calendars. It helps you to stay informed about what you are interested in and what is yet to come.

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