CUPS is a standards-based printing system for Mac OS X and other Unix-like operating systems. It provides the System V and Berkeley command line interfaces, and uses the Internet Printing Protocol ("IPP") as the basis for managing print jobs and queues. The Line Printer Daemon (LPD) Server Message Block (SMB), and AppSocket (a.k.a. JetDirect) protocols are also supported with reduced functionality. CUPS adds network printer browsing and PostScript Printer Description ("PPD") based printing options to support real world printing.
libHaru is a library for generating PDF files. It supports generating PDF files with lines, text, images, outlines, text annotations, and link annotations, compressing a document with deflate-decode, embedding PNG and JPEG images, embedding Type1 and TrueType fonts, creating encrypted PDF files, using various character sets, using CJK fonts and encodings, and basic U3D usage.
green is a PDF reader. Its main distinguishing feature is its ability to output to the Linux framebuffer (and other display methods supported by SDL). It aims to be small and efficient and not waste display space. Another rare feature is its ability to open multiple PDFs and switch between them.
mdocml is a suite of tools for compiling "-mdoc", the roff macro package of choice for BSD manual pages, and "-man", the predominant historical package for UNIX manuals. The mission of mdocml is to deprecate groff, the GNU roff implementation, for displaying -mdoc pages whilst providing token support for -man.
offrss is a standalone program that can download your favorite feeds and then show them in your favorite Web browser by spawning a simple local Web server. It will not only download the feeds' text, but also the pictures, so you will also be able to read comics strips and enjoy posts with pictures in them while offline. It can also generate PDFs from text. It remembers what you read and what you don't, and all the information stays in normal files, so you can synchronize it easily to any device that may not have an Internet connection. It can also work as a CGI to serve your feeds in your Web site, and it can update the feeds from crontab. It has few dependencies to build and can be cross compiled easily.
getxbook is a collection of tools to download books from websites. There are tools to download from Google Books' "book preview", Amazon's "look inside the book", and Barnes and Noble's "book viewer". There is an optional GUI written in Tcl/Tk, and some shell scripts using OCR to create plain text or searchable PDFs and DjVu files from the downloaded books.
PDFvcon is a GUI front-end for Ghostscript that converts the version of a PDF document. If you have software that can accept only up to version 1.4 of a PDF document and the file you have is 1.6, then this is your answer. It was created out of a need for the author to be able use some of his old Windows software.