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

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

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

Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.

Far or Near - Far or Near™ is a privacy-oriented social network that helps you connect with others who share your...

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