Emscripten: An LLVM-to-JavaScript Compiler

This is very impressive.


Emscripten

Emscripten: An LLVM-to-JavaScript Compiler
Project main site: http://kripken.github.io/emscripten-site/
Wiki site: https://github.com/kripken/emscripten/wiki
Github project: https://github.com/kripken/emscripten


asm.js

An extraordinarily optimizable, low-level subset of JavaScript.
http://asmjs.org/