Doxygen - Generate documentation from source code
Sandcastle - Sandcastle produces accurate, MSDN style, comprehensive documentation by reflecting over the source...
NDoc - NDoc generates class library documentation from .
Javadoc - Oracle Technology Network is the ultimate, complete, and authoritative source of technical information and learning about Java.
Slate API Docs Generator - Create beautiful, intelligent, responsive API documentation.
Document! X - Documentation Made Easy.