You know, now that I think about it... Node projects pretty much have all their tooling written in JavaScript already. I wonder how hard it'd be to run all that in the browser directly (right now I think this IDE is handling that on the server).
There are a number of C/C++ based node libraries... I think sass, sqlite are probably the two most popular. Any dependents of nan[0], node-gyp and node-pre-gyp are others.