EventBookings - Your Event, Your Way
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Conferize - Conferize is a web platform for finding and following conferences.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Pickevent - Personalised event recommendations based on your interests
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.