I rewrote quite a bit of the Chromium browser in Go, achieving a 10x reduction in lines of code (I stopped this project before I could reliably evaluate performance). Since Chromium uses a multi-process model, this was pretty easy: I implemented the Chromium IPC protocol in Go (I wrote a Chromium utility to emit a JSON description of the IPC protocol), and then told the privileged and unprivileged Chromium processes to use my Go subprocess rather than the original logic. My Go logic ran on both Windows and Mac OS X.