Couchmates - Transforms your roommate into your personal couch concierge

Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Prefer - Professionals you need, from people you know

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

Q Marketplace - Schedule, book, manage and pay for office services

Bigtent - BigTent is a web-based organization and communication portal for groups.