I'm probably in that camp too, I thought it was just for android and iOS still (even though I consider myself to keep up to date with these types of things).
I originally thought React Native was for all platforms, then I read their website and docs which made me realize it was only for mobile. That all went down a few weeks ago. Now, today, I find out I had it right the first time. How big a shortcoming is it of their website that it made me go away thinking it was something it wasn't when I had the right thing in mind?
You can also currently use React to share code across iOS [2], Android [3], UWP [4], macOS [5], web [6], VR [7] and a bunch of other stuff that is there mostly for fun (like React Hardware [8] and React Sketch.app [9]).
There's also experimental work on defining a set of primitives that works across all of these platforms [10].
Do you know if they have anything for linux yet?