I am using arduino here for a number of things as we progress toward finishing our observatory project. One of the items I started looking at recently was a focussing setup for one of the telescopes we have, that doesn't have a decent motor focus. I'm going to base it on a little 5v geared stepper motor I can buy for about 10 bucks, connected to an arduino type of board. My plan is to just implement the serial protocol for robofocus, then I wont need to write any drivers at all for it, just use it with drivers other folks have already implmented, windows, linux, mac, makes no difference really.
In my case, this will be for use on a C8, but, it could / would apply to any telescope, the physical mounting is the hard part. For the arduino program, it's just a case of adjusting variables etc to match whatever stepper motor / driver is used.
I'm doing the same for a dome controller I have prototyped on my desk. Arduino will drive the stepper motor, and for that one, I'll implement the maxdome protocols. With that implemented for the serial port connection, again, dont have to write any drivers for it, indi, ascom, whatever, it'll all just work. Any program that can talk to a maxdome, will be able to run the dome once it's in place.
FWIW, if your arduino based focusser has robofocus protocols implemented on the arduino serial port, then it'll work with indi / ekos right out of the box, just select the robotfocus drivers. Same can be said of any of the absolute focus gadgets that have a full open source implementation within indi, just implement that protocol on the usb connection to the host computer, and it'll all 'just work', no need to write new drivers.