This is _genius_. I have been using RegionToShare in Windows to share only a section of a widescreen monitor, but didn't have a good Mac equivalent. Now I have something that may well work _just as well_ with Windows inside Parallels (need to try that ASAP, am on the "wrong" Mac now).
Edit: A quick test shows that yes, the Windows VM sees the additional display just fine--but, alas, Parallels doesn't let me pass _just_ one physical and that virtual display to the VM, so I can't have my "personal" portrait monitor unoccupied by Windows...
I will "third" RegionToShare.. Sometimes I need to share many windows in a meeting and rather than share my entire 4k monitor, I can set up a 1080p region with RtS and put a bunch of windows in there to swap between when I'm doing my demo, and it's super useful!
Edit: A quick test shows that yes, the Windows VM sees the additional display just fine--but, alas, Parallels doesn't let me pass _just_ one physical and that virtual display to the VM, so I can't have my "personal" portrait monitor unoccupied by Windows...