TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.

Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.

Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.

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.

DownToMeet - DownToMeet is a platform to organize, find, and attend group events.