Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Mobilize - Mobilize is a scalable messaging app built for large groups.
phpBB - Raspberry Pi. The Raspberry Pi is a cheap, credit-card sized computer. The official website uses phpBB for their discussion forums. phpBB is not affiliated with nor responsible for any of the sites listed on the showcase.
Crowded Communities - The all-in-one community platform.
Flarum - Flarum is the next-generation forum software that makes online discussion fun. It's simple, fast, and free.
NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.