Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Ticket Tailor - Ticket Tailor is an easy-to-use event ticketing platform that allows event organizers of all shapes and sizes to sell tickets online.
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.
TicketLeap - Sell tickets online to your events with Ticketleap, a free and easy to use event registration and complete box office software.
Bigtent - BigTent is a web-based organization and communication portal for groups.