box2d is the physics engine behind games such as angry birds.  Although written in C++, the author sticks to pure C++ and doesn’t even use much of the STL, so this makes it easier for other developers to use tools such as emscripten to ‘compile’ the library to be used directly via javascript.  I find this quite interesting as recent performance increase in javascript runtime, led by the development of the v8 engine, means many games will eventually be able to match native speeds, hence writing a game as a stand alone web-app will not suffer much performance issues compared to native code.  The next thing I want to learn is how to use the physics library in javascript and combine physics with beautiful vector-based graphics that can be generated with modern browser.