With what? Rails? Doesn't that require generating a whole "project" (whatever that is) with a bunch of directories and files and then figuring out where everything is and...

PHP requires opening index.php and typing "hello world". Obviously that's not going to work anywhere else, but something like Flask (or Sinatra) is much closer.

Deployment, maybe. The biggest stumbling block is that no matter how magical a deployment solution anyone invents, it's worthless unless there are free/cheap hosts that come with it installed and have cPanel integration.