Windows RT does NOT do this.. They have a few very limited APIs for IPC, such as Search.. other than that, it's very tied down. Even so much so that it's impossible to make a universal file browser. You have to declare ahead of time which file extensions your application should be capable of opening

Think of Mac OS Automator for mobile devices (let's name it "Task Composer"), letting you assemble whole workflows based on pipes. But this would potentially harm any AppStore interests, so this will never happen, not on any of the current platforms.

(Edit: This would also afford to expose system calls to the end user, being the end of consumer haven.)