One of the best things about OS X (as it used to be called) is that the runtime was accessible not just from Objective-C, but also from ruby or python or JavaSc

One of the best things about OS X (as it used to be called) is that the runtime was accessible not just from Objective-C, but also from ruby or python or JavaScript. It was very cool to be able to fire up a repl and go exploring in the innards of the various frameworks.