Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.
Mobilizon - A free and federated tool to get our events off Facebook
CooMeet - CooMeet is one of the best and leading next generation of video dating web-based application specially designed for those users who want to talk online to people they have never met.
Hinge - Find people you want to date through your friends on Facebook.
Agorakit - Agorakit is web-based, open source groupware for citizens.