Xpdf has been ported to various other (non-UNIX and non-UNIX-like) systems:
!PDF is a port to RISC OS (for the Acorn), now maintained by Colin Granville, originally done by Leo Smiers.
BePDF is a port to BeOS by Michael Pfeiffer.
Apdf is a port to the Amiga by Emmanuel Lesueur.
Pdf is a port to EPOC (the Psion operating system) by Sander van der Wal.
qpdf2 is a port to OPIE (embedded Qt on iPAQ/Zaurus handhelds) by Philip Kohn.
PalmPDF is a port to PalmOS 5.x.
Here are some other tools based on the Xpdf code:
pdftohtml converts PDF files to HTML. By Mikhail Kruk; originally written by Gueorgui Ovtcharov and Rainer Dorsch.
SWF Tools includes PDF2SWF, which converts PDF files to SWF (Flash) animations.
PdfSearch is a Python-based utility for searching PDF files.
PDFKit is a PDF rendering framework for GNUstep.
Applets in PDF adds Java applet support to Xpdf.
User submitted patches for Xpdf:
Add support for Unicode outline entries (requires glib and pango). By Sven Verdoolaege.
A version of Xpdf patched to use gettext for internationalization