Software

Apago
Develops software solutions for graphic arts and prepress markets, conversion tools for PostScript, PDF and raster workflows, custom applications for prepress, document management (COLD), large format and variable printing markets. Image compression including fractal, wavlet and JPEG 2000. Plug-ins for Acrobat, Quark and Photoshop.
http://www.apagoinc.com

Ghostscript, Ghostview and GSview
Free for non-commercial use programs to render PostScript documents, links to related utilities.
http://pages.cs.wisc.edu/~ghost/

Ghostscript.com
A news and community site for the Ghostscript software.
http://www.ghostscript.com/

GNU Enscript
Converts ASCII files to PostScript and spools generated PostScript output to the specified printer or leaves it to file. [GPL]
http://www.codento.com/people/mtr/genscript/

GSview
A graphical interface for Ghostscript, to display postscript documents on several platforms.
http://pages.cs.wisc.edu/~ghost/gsview/

GV
Front end for ghostscript to display PostScript and PDF documents.
http://wwwthep.physik.uni-mainz.de/~plass/gv/

Le GNU a2ps
Filter to convert many file types to PostScript.
http://www.inf.enst.fr/~demaille/a2ps/

PostScript Interpreter (RIP) and OEM SDK
Rapport is a PostScript technology developer based in the UK and the creator of InkWell - A high performance PostScript compatible interpreter and Software Development Kit for OEMs. Add PostScript capability to any system: printers, servers, controllers and applications.
http://www.rapport.ltd.uk/

PostScript Tools
Collection of utilities for printing and formatting. With documentation and source.
http://www.math.utah.edu/~beebe/software/postscript-tools.html

PreScript
Utility for extracting text from local PostScript files.
http://www.nzdl.org/html/prescript.html

PSUtils
A set of command line utilities for manipulating PostScript files in various ways, including multiple pages per sheet, book sorting, resize pages, and splitting files. Documentation and downloads.
http://www.tardis.ed.ac.uk/~ajcd/psutils/

RoPS
A Microsoft Windows implementation of the PostScript programming language interpreter. [Free and commercial versions]
http://www.rops.org/

YARC Systems Corp.
Licenses PostScript software to OEMs, makes end-user products, since 1980s, mainly for publishing and Macintosh markets, but recently offering Linux based server technology.
http://www.yarc.com/