NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.
Mobilize - Mobilize is a scalable messaging app built for large groups.
vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
Crowded Communities - The all-in-one community platform.
BoonEx Dolphin - Dolphin is an open-source software for creating custom social networks and web communities.
Spot.IM - Spot.IM offers a set of tools and technology for your online community management.