There is only one file type that uses the .OS extension:
ObjectScript Source File
An OS file is a source file that contains ObjectScript code, which is a general purpose object-oriented programming language. It stores an executable script, which includes a list of commands and functions written in ObjectScript.
If you have ObjectDevel installed on your computer you can simply double-click the OS file to open it in ObjectDevel.
OS files can be converted into a standalone ObjectScript application by bundling files into a .JAR file. This makes it simpler to distribute a standalone ObjectScript program. To do this, selectand select the JAR file where you want to save the ObjectScript application.
Updated: September 7, 2018