This is a link to a Google code research project looking at making it possible to run native code in a browser.
This is the second such project I have seen, I have blogged before about Adobe's effort in the same area.
However, Google have ported Quake to the browser which gives them extra points if you ask me.
Seriously, I think this is a really interesting project. The possibilities could be only limited by the tools supplied for developers to use.
There is an interesting video about the project at the above link.