I have recently discovered a web application which allows you to run iOS apps in the browser. Said application is Pieceable Viewer.
I was curious about how it works and is able to do its job so I did a quick google search and found a rather short answer on Quora:
It looks like they are running multiple instances of the iPhone Simulator and piping it through VNC. They've also hooked (method swizzled) a number of messages such as openURL: which would escape out of the current application.
This was interesting, but I wonder if anyone could give a bit more info on how exactly they are able to have multiple instances of the iOS Simulator open and being able to pipe each one through VNC.