A Windows 10 tablet (I can't name one, but some probably exist) has this out of the box with the wireless screen projection (win+K). I had to do this laptop to laptop to projector for a lightning talk once after the first laptop had a broken display port adapter - surprisingly fast to setup and 0 latency.

I'd be surprised if something didn't exist for Android tablets. But if you have an old laptop laying around, maybe throw w10 on it and see if it works?

Not all Win 10 tablets support the wireless projection. I think you can do it with a higher end one like a Surface Pro, but you can't with less powerful ones like the Asus Vivotab 8. You'll get an error message having to do with not meeting the minimum requirements.

On the other hand, you can use something like Synergy, but that's not quite the same thing.

I think this is https://en.m.wikipedia.org/wiki/Miracast ?

I use Spacedesk for this. It supports Windows as the server and Android, iOS, Windows and web browsers as clients (extra displays). It's still in beta, but it works almost flawlessly. If your wifi chips are good quality, the latency is almost unnoticeable.

Thx. I was looking for a Win / Android solution. I'll have to check this out.

yeah if you have an iOS tablet, check out duet. works well on my ipad pro