A Note to Developers The Ultimate Notification System for OS X. Growl is the easiest way to know what's going on with your applications. Growl Source Installation Requirements In order to build Growl, you will need: OS X Lion - 10.8. Xcode 4.6.1. You can download older versions of Xcode from the developer downloads page. A tool to pull down a clone of the repo, the mercurial client. Click here for