HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Documize - Enterprise-grade wiki and knowledge management platform
WinCHM - Creating CHM file, Make CHM file, Web Help. WinCHM Pro - Help authoring software (CHM, WebHelp, DOC, PDF) . With this powerful tool you can not only create chm file from scratch, but also convert a set of existing HTML files to a chm file.
HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
Dokit - The solution for disseminating know-how: work instructions, procedures, knowledge base, documentation techniques, product support, wiki enterprise.
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.