FileInfo.com - The File Extensions Resource

.ION File Extension

File Type	4DOS File Description
File Format	File
Common?	No
File Description	Describes the contents of another file; typically hidden and used in the MS-DOS command line; sometimes named "descript.ion"
Program(s) that open ion files	Windows: MS-DOS command line or a text editor, such as Notepad

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