My Belkin 4-port KVM, this was one of my first ebay purchases back in 1999.

This is actually a fantastic KVM for vintage systems (and it’s still cheaply available used).  It has PS/2 and serial mouse ports, and will translate between the two, so I can have this hooked up to a mix of PCs with serial or PS/2 ports and control them all with a single PS/2 mouse, so it’s great for my workbench.