Icon image file used for Windows file and folder icons; saved in a bitmap image format that can be opened by various image editors.
Windows icon files more commonly use the .ICO extension and may include multiple resolutions of the icon; icon files in Mac OS X use the .ICNS extension.
Program(s) that open icn files
Mac: Adobe Photoshop with IconBuilder plugin; XnView Windows: Adobe Photoshop with IconBuilder plugin; ACDSee Photo Manager; XnView
Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/icn
