Are you thinking of the display-switch[0] script? Achieves K/V/M-switching with only a cheap USB-switch for hardware K/M-switching, and then this script detects such peripheral switching and emits DDC-commands for monitors to switch accordingly.

I saw it posted here on HN[1], and have been using it since then with great success.

[0] https://github.com/haimgel/display-switch [1] https://news.ycombinator.com/item?id=29608967