"Native Client is an open source technology for running native compiled code in the browser, with the goal of maintaining the OS portability and safety that people expect from web apps. Native Client expands web programming beyond JavaScript, enabling developers to enhance their web applications using their preferred language. This technology can be implemented in any browser and is not tied to a specific CPU architecture."
http://code.google.com/p/nativeclient/
http://code.google.com/chrome/nativeclient/