Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
TicketPeak - Online Ticketing Software
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Audience View - Audience View is a cloud-based ticketing solution created for the performance arts industry and suitable for both profit and commercial uses.
Meetabit - All the local tech and startup meetups in one place - easy to organize & attend
TicketingHub - Next generation of Ticketing