AppleScript - Open Scripting Architecture

An important aspect of the AppleScript implementation is the Open Scripting Architecture (OSA). Apple provides OSA for third-party scripting/automation products such as QuickKeys and UserLand Frontier, to function on an equal status with AppleScript. AppleScript was implemented as a scripting component, and the basic specs for interfacing such components to the OSA were public, allowing other developers to add their own scripting components to the system. Public client APIs for loading, saving and compiling scripts would work the same for all such components, which also meant that applets and droplets could hold scripts in any of those scripting languages.

Under Mac OS X, the JavaScript OSA component remains the only serious OSA language alternative to AppleScript, though the Macintosh versions of Perl, Python, Ruby, and Tcl all support native means of working with AppleEvents without being OSA components. The MacRuby development roadmap shows that OSA conformance is planned in version 0.6.

One of the most interesting features of the OSA are "scripting additions", or OSAX for Open Scripting Architecture eXtension, which were based on Hypercard's External Commands. Scripting Additions allow programmers to extend the function of AppleScript. Commands included as Scripting Additions are available system wide, and are not dependent on an application. Mac OS X includes a collection of scripting additions referred to as Standard Additions, which extends the function of AppleScript with a variety of new commands, including user interaction dialogs, reading and writing files, file system commands, date functions, text and math operations.