[bennofs]

On Linux, I've used https://github.com/rhofour/evdi-vnc to make a secondary screen that you can connect to with any VNC client.

[franga2000]

Boy would this comment have saved me a lot of time had it been posted on the original discussion a couple of days back!

I did eventually find that project, but only after having written what is essentially the non-VNC half (creating and managing evdi displays) of it from scratch...