macOS can switch input sources per app or by shortcut, but not natively per keyboard. If your keyboards have different layouts, you end up switching by hand every time you move between them, or typing the first few characters in the wrong layout and fixing them after.

Keychange is a menubar app. It lets you assign an input source to each connected keyboard, and it switches the moment you start typing. Keyboards are identified per VID/PID and mappings survive unplugging.

I used autokbisw for years, which solves the same problem from the command line and solves it well. I wanted the mapping visible and configurably more easily. Keychange implements two things beyond that: it can optionally switch before the key press is delivered, so even the first character after a switch comes out right and it has strategies what to do when the input source is changed by other apps.

It needs Input Monitoring permission to detect which device a keystroke came from. Nothing is stored or sent anywhere. The only network request it makes is the update check. Free, MIT licensed.

https://keychange.dev https://github.com/dennistimmermann/keychange

It's a brand new app, so any and all feedback is welcome.