The cocoa vocabulary implements a Factor-Cocoa bridge for macOS (GNUstep is not supported).

The lowest layer uses the C library interface to define bindings for the various functions in Apple's Objective-C runtime. This is defined in the cocoa.runtime vocabulary.

On top of this, a dynamic message send facility is built:
Calling Objective C code
Subclassing Objective C classes

A utility library is built to facilitate the development of Cocoa applications in Factor:
Cocoa application utilities
Cocoa file dialogs
Cocoa pasteboard utilities
Cocoa view utilities
Cocoa window utilities