Yes, operating systems were also in my mind. Great examples about Plan 9 and BSD.
I confess I didn't write any piece of code in Go, but read sometimes here a lot about it.
So I'm curious what do you think are the most innovative things Go brings to programming languages?
Go attempts to bring the original Unix and Plan 9 innovative philosophy to the other systems, most importantly: simplicity, and doing things sanely from the start, not in a complicated fashion. You can find lots of material about Go on the internet, but one could list features like compact syntax, fast compilation, easy deploying (statically linked binaries), and easy networking and concurrency features (CSP). These are not necessarily "new" innovations but they are rarely utilized by other tools to same extent (Plan 9 being notable exception).