Ghostscript
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Ghostscript is an implementation of the Adobe PostScript page description language. It includes functions to render PostScript and PDF, both to monitors and printers.
Originally developed by Aladin and released under the "Aladdin Free Public License", the copyright is currently owned by artofcode LLC. Two versions are released one after the other, the first for commercial use with the original AFPL license, and another with the GNU license as GNU Ghostscript.
The GNU version is also used as the basis for a GNU Display Ghostscript, which adds the functionality needed to fully support Display PostScript.