Vanilla Forums - Build an engaging community forum using Vanilla's modern cloud forum software.
Documize - Enterprise-grade wiki and knowledge management platform
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
PunBB - PunBB is a fast and lightweight PHP-powered discussion board.
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.