A proof-of-concept port of XaoS, a real-time fractal zoomer, to Native Client is now available in the
Chrome Web Store. The (slightly dated) case-study describing the details of the port can be found here, but in case of doubt it is best to consult the actual source code and patches in the naclports repository. The port should compile fine with recent versions of both the gcc based "NaCl" and the clang based "PNaCl" toolchain.
Work is underway for an update to Robby Roto and the underlying Mame engine which can likewise be found in the
Chrome Web Store. Stay tuned!