title: What's that app or library that allows one to add functionality to cocoa apps?
body: <p>I recall reading about an application or library that allows to add some functionality to Cocoa apps.<br>
  I found it when searching for an application for using mouse gestures in Finder and applications other than browsers, but I didn't pay too much attention to it because I didn't know Objective-C or Cocoa at the time.<br>
  Do you have any idea of which one could it be?</p>