ApiGen!

Doxygen is a tool for generating documentation from annotated C++ sources, as well as other popular programming languages like C, Objective-C, C#, PHP, Java, Python, IDL (CORBA, Microsoft, and UNO/OpenOffice flavors), Fortran, VHDL, Tcl, and to some extent D.

Slate - beautiful static documentation for your API.

PHP documentation generator based on docblock parsing.

LDoc is Lua documentation generator intended to be compatible with LuaDoc and thus follows the pattern set by the various Doc tools:

LuaDoc is a documentation generator tool for Lua source code. It parses the declarations and documentation comments in a set of Lua source files and produces a set of XHTML pages describing the commented declarations and functions.

At Qmino (the company that creates Miredot), we've written hundreds of REST APIs. We design and redesign until our APIs are an joy to use.

Shins (Shins Is Not Slate) is a port of Slate API Docs Generator to JavaScript / Node.js , beautiful static documentation for your API.