Doxygen - Generate documentation from source code
Slate API Docs Generator - Create beautiful, intelligent, responsive API documentation.
Javadoc - Oracle Technology Network is the ultimate, complete, and authoritative source of technical information and learning about Java.
Sandcastle - Sandcastle produces accurate, MSDN style, comprehensive documentation by reflecting over the source...
Aglio - API Blueprint renderer
CppDoc - CppDoc generates HTML documentation for C++ classes, based on your source code and special comments...