AppleScript: The Definitive Guide, 2nd Edition

Applet and Droplet

An applet is an application with very little graphical user interface, consisting essentially of a compiled script along with a minimal amount of standalone executable code, called the bootstrap code, along with some other resources necessary to make the application scriptable. The bootstrap code, which runs when the applet is launched, simply summons a scripting component called the Script Application Component ; this component does the rest, handing the compiled script over to the AppleScript scripting component for execution, and taking care of such application-like functionality as putting up the applet's menu and its description window if there is one. Thus an applet is a tiny application which, when launched, runs a compiled script embedded within it. A script editor application will allow you to make an applet as simply as saving a compiled script file, just by choosing applet format (called "application") when you save (or choose File → Save As).

When you save your script as an application, the script editor application looks to see whether it has an open handler. If it does, the application becomes a droplet . A droplet is just like an applet, except that it has a different creator type (the creator type for an applet is 'aplt', while for a droplet it's 'dplt') and a slightly different icon; functionally, the difference is that a droplet does something when file or folder icons are dropped onto its icon in the Finder. Typically, a droplet responds to ...