Emscripted Ruby is a build script that uses Emscripten to compile Ruby MRI 1.8.7 for use in a browser. The main difference is the conversion from C to C++ and the switch from setjmp/longjmp (which can't be implemented in JavaScript) to C++ exceptions.
The project is in its infancy. Right now it suffers from a crash due to an LLVM's miscompilation of the Ruby garbage collector, and have numerous deficiencies, especially in handling Bignums.
The build script is licensed under the MIT license. The modifications follow Ruby's GNU GPL2 license.