Play Dune 2 directly in the browser, as far as i remember this game was the first in its genre. This is a port of Open Dune, an open source implementation of the classic real-time strategy game Dune II.
Emscripten is an LLVM to JavaScript compiler. It takes LLVM bitcode (which can be generated from C/C++ using Clang, or any other language that can be converted into LLVM bitcode) and compiles that into JavaScript, which can be run on the web (or anywhere else JavaScript can run).