Simultaneous output of 3 cameras divided equally on one monitor

I have a need to get the simultaneous output from 3 cameras equally displayed on 1 monitor.. (in real time, Not Sequentially displayed). I know there are systems with 4 cameras that split the screen of a monitor into 4 grids, but my application requires 3 cameras on 1 monitor. I will also need to record the monitor output.

Can you stir me to a product or source of the required equipment as described above? I am willing to Homebrew in the case you can provide some schematic.