HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
Documize - Enterprise-grade wiki and knowledge management platform
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
Boardist - Personal workspace for all the data
Dozuki - Dozuki is a web-based tool for creating and distributing step-by-step documentation.
Twake - Be more productive with Twake : the collaborative work platform to organize and manage all your projects on a single platform.