Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
CoFoundersLab - Meet 250,000+ entrepreneurs online
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Peanut - Peanut is a Mobile Application for moms developed and published by Peanut App Ltd.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Flingster - Flingster lets you find local flings for random dates with people from your area.