From: John Joyce <dangerwillrobinsondanger@...>
Date: 2007-12-30T07:42:23+09:00
Subject: Re: Can Ruby be a keylogger on Win/Mac?

You're going to have a hell of a time building a keylogger for OS X.
You'll want to look into the input managers. The same thing for  
building an Input Method for another language.
With that part of Cocoa, you could definitely monitor input.
Beware though, the docs are dense, and there is big learning curve.
Also, input methods tend to cross the gap between Cocoa and Carbon  
(basically between Obj-C and C frameworks)

You might try an AppleScript layer that intercepts and then passes  
the same keystrokes... (System Events)