Mobilize - Mobilize is a scalable messaging app built for large groups.
NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.
Ning - Ning is the social platform for the worlds interests and passions online.
vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
Spot.IM - Spot.IM offers a set of tools and technology for your online community management.
Invision Community - Invision Community is a flexible, integrated set of apps for building communities on the web.