Xprint

Xprint is an expanded printing system which allows X11 programs to use devices such as a printer or fax.

It also allows to interpret documents in PostScript, PDF, PCL etc. formats. This works in which one creates a virtual printer to send again instead of the expression to the printer, send it to a program, which then applies the expression as a document.

Xprint is developed under the GPL. It is now considered outdated.