Well a quick search brought up a few things. It could be a
KEY AntiVir PersonalEdition License Key File (AntiVir PersonalProducts GmbH)
KEY Keynote Presentation Wrapper Folder (Apple Computer)
KEY Business Key Accounting File (Universal Systems)
KEY Program Security or Registration File
KEY TBAV File
KEY Sentry 2020 Encryption File
KEY Forecast Pro Datafile
KEY National Construction Estimator 32 Costbook Key File
KEY Keyboard Definition File
KEY Infinity Game Engine Directory of Resources, Locations and Types (BioWare Corp.)
KEY FractInt Demo Script
KEY Diablo II Key File (Blizzard Entertainment)
KEY DataCAD Icon Toolbar File (DATACAD LLC)
KEY ArcView Geocoding Matching Keys (ESRI)
KEY OS/2 Archive .KEY-file
KEY Top Secret Crypto Gold (TAN$TAAFL Software Company)
So there are many things it could be. What is the file you are trying to open and maybe we can help find the app to use.
