[grishka]

> I wonder if there is a standalone library to do this on other platforms.

There's a thing called Cycript for jailbroken iOS that, among other features, allows you to attach to any process and then gives you what's basically a command line interface to the objective-c runtime. It's a godsend for reversing iOS apps.

It should also be trivial to implement a similar tool for Android using Xposed framework.