My home is connected with a mix of X-10, Z-Wave, Insteon, ISY, Echo, and Philips Pronto. Unbelievably, thanks to ISY and a couple of Raspberry Pis, everything works.

 

I hired someone to redo the bathroom and specifically requested either extra deep boxes, or use of junction boxes to join lines - not the switch box. Naturally, I now have 3 lines plus 4 loads coming into a 4-gang box. That rules out my stash of  X-10 switches - they don't fit. And it's too late to change. Yes, mea culpa, I didn't inspect the boxes.

 

Does anyone have a recommendation of a switch, compatible with ISY, that will fit in a very tight box?

There's always room above and below devices to run the wires carefully. Also each side is available.

 

If you trim the wires somewhat and remove enough insulation to tightly twist the wires together to enable a smaller wirenut after trimming the twisted wires and folding them neatly into place, then you should be able to fit Insteon switches. If you absolutely can't fit all four devices, then you can replace one or more switches with KPLs and add a Micro Module at the load box, as needed

 

Just don't cut the now unused load wires too short so they can't be used in the future. You can save additional room by taping over the unused ends instead of capping them and also not connecting them at the other end. Tape there too, for safety.