ICNS

ICNS is the native icon format of Mac OS X.

It goes by many other names, including Apple Icon, Macintosh Icon, Mac OS Icon, Macintosh OS X Icon, Mac OS X Icon Resource, Mac OS icns Resource, and IconFamily Resource.

Supported image sizes are 16, 32, 48, 128, 256, 512, and 1024 pixels square.

Identification
Files begin with ASCII characters " ".

Related formats
Some ICNS files contain icons in the form of embedded PNG or JPEG 2000 files.

Software

 * libicns
 * XnView

Links

 * Wikipedia article