Doxygen - Generate documentation from source code
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.
DocFX - A documentation generation tool for API reference and Markdown files!
Kchmviewer - Kchmviewer is a free, open-source CHM (MS HTML help) and EPUB viewer for Unix, Mac and Windows...
Natural Docs - Natural Docs is an open-source documentation generator for multiple programming languages.
Microsoft HTML Help - Microsoft HTML Help is the standard help system for the Windows platform.