Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Hoodline - Hyper-local SF news from the former editor of TechCrunch
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Circa - Find a time that works for everyone, in every time zone
Bigtent - BigTent is a web-based organization and communication portal for groups.
The Tab - Hyperlocal news site written by student journalists