@alucard555 yes, there is a very very simple example of a browser-based game (Asteroids in 250LOC!) that could work in a desktop app via Electron or something:
https://github.com/amark/gun/blob/master/examples/game/space.html
You can play the game (arrow keys to move, space to fire a shockwave, doesn't work on mobile or small screens) here:
http://gunjs.herokuapp.com/game/space.html
With regards to Unity3D specifically, you would need a JavaScript bridge. I myself have not done Unity3D development myself, but I have (?) heard (?) it supports JavaScript? Or some variant of it?
GUN by itself is plain vanilla JS, the only porting UnityScript may need is changing the default localStorage and WebSocket adapters (these are modular and can easily be switched out for something Unity supports).
However I do not have enough Unity3D experience to speak on this matter. (I just looked up Firebase's Unity support, and noticed that it is not JS based, it is C++. This may mean JS is incompatible with Unity?)