I'm successfully sharing my Ubuntu Desktop with my Mac Book, using VNC.
My Mac Book Pro is on the right, my external monitor is in the center, and I have an Ubuntu Laptop on the left as in this image:
While using the Mac, I'd like to be able to slide my mouse to the left of my centre external monitor, so I can think of the Ubuntu system as an additional monitor, as it were.
I have been able to do this from within Ubuntu in the past, by setting up a virtual monitor using "x2x -south -to :1"
I'm curious as to whether this functionality is possible using my Mac.
I've found the following which are close, but "no-cigar" https://superuser.com/questions/276766/create-virtual-external-display-for-vnc-control
I've found the following software that might work, though not free: http://symless.com/synergy/