Adobe Illustrator much like any other Adobe software supports the exporting of files to PostScript for printing, which is exactly what ai to ps conversion represents. You can usually access this via dedicated Export function, or with a Virtual PostScript printer installed. Such PS files are meant for printing not for further editing although they can be imported to other programs as well.
Open AI file Open PS fileA vector-based drawing software
A universal vector graphics translator
A vector graphics converter for various Linux distributions