Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Facebook Local - Discover places to go and events happening near you
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
TechEvents.co - Tech and startup events aggregator
Bigtent - BigTent is a web-based organization and communication portal for groups.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets