Guestboard - Lead powerfully-organized group events with Guestboard – a modular event platform that gives groups of 10-1000+ people a central space to coordinate, build excitement, and save money. No more crazy email threads. No more massive group texts.
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.
Mobilizon - A free and federated tool to get our events off Facebook
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
TicketSource - Free, easy to use online ticketing for your events.