Kialo - Kialo is the platform for rational debate. Empowering reason through friendly and open discussions.

Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.

argunet editor - Argunet Editor is a free argument map editor for analyzing and visualizing complex debates.

Loomio - Loomio helps groups of people make decisions together, online.

UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system

DebateArt.com - DebateArt is a unique and growing community committed to the idea of exchanging views and perspectives through debating.