I'm full-time OSX user/developer, but if Rails is really your sticking point, shouldn't the linux subsystem make Win10 at least viable for a trial? Or, frankly, anything that can run VMWare or Virtualbox?
Should be great when it comes out of beta, though - a good terminal and we'll be all set.
you can install what you want on macOS and you can install what you want on Windows. Both have custom terminal apps
It's not listed in his requirements and Win10 may satisfy him.
There are lots of free things in life that have an inferior free alternative or only free alternatives and this may be one of them.
And I said you don't need to pay for anything if you want to do Rails programming. In fact, here, the "inferior alternative" for this task may be the proprietary one.
Another thing would be using his computer for gaming. In that case, I wouldn't object, of course.