zlib is designed to be a free, general-purpose, legally unencumbered, lossless data-compression library for use on virtually any computer hardware and operating system. The zlib data format is itself portable across platforms. Unlike the LZW compression method used in Unix compress(1), the compression method currently used in zlib essentially never expands the data. (LZW can double or triple the file size in extreme cases.) zlib's memory footprint is also independent of the input data and can be reduced, if necessary, at some cost in compression.
di is a disk information utility that displays everything that df does and more. It features the ability to display your disk usage in whatever format you prefer. It also checks the user and group quotas, so that the user sees the space available for their use, not the system wide disk space. It is designed to be highly portable across many platforms and is great for heterogenous networks.
pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info written by Photoshop 5.0 as well as the erroneous iCCP chunk written by Photoshop 5.5.
IP Tables State implements the "state top" feature from IP Filter for IP Tables. "State top" displays the states held by your stateful firewall in a "top"-like manner. Since IP Tables doesn't have a built-in way to easily display this information once, an option was added to iptstate to do this.
gif2png is a simple command-line utility to convert images from GIF to PNG format. It automatically preserves transparency, interlacing and text comments, and it can do multiple images in one command (e.g., gif2png *.gif). The distribution also includes a web2png script that can be used to convert an entire web tree; it calls gif2png to do image conversions, then patches IMG SRC tags correctly in referring pages.
clapf is a high performance email content filter application. It includes a statistical (inverse chi-square) antispam module, an interface to several anti-virus products, and a Web UI (including a spam quarantine) written in PHP. It supports virtual users, URL- and IP-address blacklists, whitelists, LDAP directories, policy groups, minefield, and many more features. clapf can be used as an after queue content filter with Postfix (including as an appliance) and Exim or via the maildrop local delivery agent (LDA). It's also ideal to act as a spamfilter appliance in front of an Exchange server.
libunibreak is an implementation of the line breaking and word breaking algorithms as described in Unicode Standard Annex 14 and Unicode Standard Annex 29. It is a superset of, and supersedes, liblinebreak. It is designed to be used in a generic text renderer. FBReader is one real-world example.