Beaglewing
A keyboard, mouse, and clipboard bridge where the second computer sees real USB hardware.
Slide your cursor off the edge of your Linux desktop and it comes out on the machine next to it, carried by an actual USB device, not a software agent. Think Synergy or Barrier, except the controlled machine needs nothing installed, nothing configured, and no network access to you at all. From its point of view, somebody plugged in a very good keyboard and mouse.