EventsApp - A simple concise app for creating and sharing events.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
1up Events - Corporate events as a service
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Eventjoy - The Easiest Way To Organize An Event
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets