FileInfo.com - The File Extensions Resource

.ARR File Extension

File Type 1	Amber Graphic File (Most common)
File Format	File
Common?	No
File Description	Bitmap image used by microscopes; supports 256 shades of gray
Program(s) that open arr files	Mac: Lemke Software GraphicConverter

File Type 2	Advanced RAR Password Recovery Project
File Format	Proprietary File
Common?	No
File Description	Password recovery project created with Elcomsoft Advanced RAR Password Recovery (ARPR); saves the current state of the password recovery operation so that it can be resumed at a later time.
Program(s) that open arr files	Windows: Elcomsoft Advanced RAR Password Recovery (ARPR)

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/arr