OnShape does not have a desk top app. It runs in a browser but it works very well. For me, it does not really feel like it is running in a browser, at least not in my current fast computer. F360 on the other hand seems a little clunky at times when running in the browser. OnShape has an iPad app that has a very similar look and feel. I have modified a simple drawing on iPad and it was not too bad. I think that on an iPad with their pencil stylus, it might be just as easy to use. Without paying for a pro license, I am not away if there is a way to store OnShape drawings locally but you can export them to other formats.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.