From the FAQ page on pdf995.com:

The default configuration of Pdf995 uses the registered Postscript to 
PDF converter on your system, but you may choose to have the program use 
the GPL Conversion module we offer as a free download. The GPL 
Conversion module includes a partial version of GNU Ghostscript. Pdf995 
supports other Postscript-to-PDF converters. GNU Ghostscript is 
distributed under the GNU General Public License. You may obtain the 
source code for GNU Ghostscript here.

Again, I'm figuring this out as I go along, but it seems pdf995 is in 
the same family as the others (bullzip, pdfcreator, cutepdf, etc.)