There is only one file type that uses the .OSX extension:
PowerPC Executable File
An OSX file contains a program header for a Power PC application and is saved in the PEF (PowerPC Executable Format) binary executable format. It can be run directly in Mac OS X on PowerPC-based Macintosh computers or via Rosetta on Intel machines. OSX files may also reference other files that are required for the program to run.
OSX files are typically generated by Adobe Director.
NOTE: Running "file" on an ".osx" file in the Macintosh Terminal produces "Header for PowerPC PEF executable file."
Updated: January 15, 2019