This is also by far the #1 killer feature for me in Windows 10 Anniversary Update.

You can now use other Windows 10 PCs as wireless displays and project to them in any display configuration as long as they're on the same local network. It can also reroute audio output from the host to projected PCs, and even reroute input (mouse, keyboard, touchpad, touchscreen(!), pen(!), etc) from projected PCs back to the host.

From my experience so far it has worked impeccably well. There is a bit of input lag and the occasional compression artifact, so hardcore gaming is definitely out of the question, but it's more than good enough for regular media consumption and browsing.

I really can't wait to see something like this land in more OSes.