phpman is a PHP/MySQL-based system to publish your
manuals and documentation. It supports multiple
languages, a Web-based HTML editor (spaw), and
real time PDF generation.
ObjcDoc is a tool for documenting Objective C class libraries. It can parse Objective C source code and creates HTML output files containing class documentation extracted from special comments inside the source code (somewhat similar to JavaDoc).
Manumission is a commandline utility which creates HTML Help files. These files are viewable using either Microsoft's help viewer or xchm. No configuration is required, and options default to reasonable values.
Aephea is a text-based authoring tool for HTML. It enforces well-formedness with a simpler and stricter TeX-like syntax and provides useful extensions and abstractions with facilities for adding new ones. It emphasizes a single unified approach that stays close to HTML itself and promotes and utilizes CSS extensively. Abstractions such as dictionary stacks, arithmetic, and iteration are part of Aephea.