FileInfo.com - The File Extensions Resource

.HEX File Extension

File Type 1	Hexadecimal Source File (Most common)
File Format	File
Common?	No
File Description	Contains settings, configuration information, or other data saved in a hexadecimal format; may be stored in either a binary or text format. NOTE: Binary hex files can only be opened with hex-editing programs; text-based hex files can be opened and edited with a text editor.
Program(s) that open hex files	Mac: HexEdit; HexEditor Windows: Heaventools FlexHex; Hex Workshop Hex Editor; Cygnus Hex Editor; HHD Hex Editor

File Type 2	BinHex Encoded File
File Format	Standard File
Common?	No
File Description	File encoded with an early version of BinHex (binary-to-hexadecimal) encoding software; used for converting files to a text format that could be sent via e-mail without being corrupted; typically takes up more space than the original file. The BinHex program is only available for the Mac; newer versions of the program save BinHex files with a .HQX extension rather than ".hex."
Program(s) that open hex files	Mac: Smith Micro StuffIt Deluxe for Mac; Mac Binary Converter; UUDeview Windows: Smith Micro StuffIt Deluxe for Windows; UUDeview Unix: UUDeview

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