TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.