The C++ version of Bullet can be build using the Native Client compiler and it runs full-speed in the Google Chrome web browser, without plugin.  Just check your Chrome About Box to make sure the version is 15 or later and you can check out the live demo.

The Bullet C++ source code didn’t need any modification, and it compiled out-of-the-box using the premake4 generated Makefiles. Check out the Native Client for Dummies article for more information.