Welcome to Ghostscript, an interpreter for the PostScript language and for PDF.
The leading edge of Ghostscript development is under the GNU Affero GPL license.
With immediate effect development of Ghostscript and MuPDF is moving to the GNU Affero GPL license. Future releases, including the one scheduled for February 2013 (9.07) will similarly be released under the GNU Affero GPL license.
We have also started collating a Frequently Asked Questions page. It is early days, but may prove useful:
Other page description languages:
A user-friendly viewer: