Small sample cross-platform networking library

http://www.libsdl.org/projects/SDL_net/

SDL audio library and player for some popular sound file formats

http://www.icculus.org/SDL_sound/

Library to use TrueType fonts to render text in SDL applications

https://www.libsdl.org/projects/SDL_ttf/

"Simplified" DocBook XML DTD

http://www.oasis-open.org/docbook/xml/simple/

A utility for generating secure passphrases

http://www.core-dump.com.hr/?q=node/28

Extensive german HTML reference

http://www.selfhtml.org/

Reliable, highly configurable mail transfer agent with utilities

https://www.sendmail.org/

Serf HTTP client library

https://serf.apache.org/

Manage utmp/wtmp entries for non-init X clients

Set the keyboard using the X Keyboard Extension

https://www.freedesktop.org/Software/xorg

Generates groff and HTML from linuxdoc and docbook SGML documents

Interoperability between desktops and collaborative environments

http://oscaf.sourceforge.net

MIME types database from the freedesktop.org project

https://www.freedesktop.org/wiki/Software/shared-mime-info/

Generic script compiler

http://www.datsi.fi.upm.es/~frosal/frosal.html

Font dumper for the X font server

https://www.x.org/

HTTP regression testing and benchmarking utility

http://www.joedog.org/JoeDog/Siege

Secure Internet Live Conferencing (SILC) network toolkit

http://www.silcnet.org/

SixXS IPv6 TIC+ tunnel broker heartbeat client

http://www.sixxs.net/tools/aiccu/

Fully automated, active web application security reconnaissance tool

http://code.google.com/p/skipfish

A full-screen X11 task-switcher like Apple's Expose

http://thegraveyard.org/skippy.php

SLang-based newsreader

http://slrn.sourceforge.net/

SIP scanner and identifier

http://www.wormulon.net/

S.M.A.R.T. disk monitoring tools

https://www.smartmontools.org

Samba-LDAP management and support tools

https://gna.org/projects/smbldap-tools/

Free MPEG1 video player library with sound support

http://www.lokigames.com/development/smpeg.php3

Session Manager Proxy

Fast compressor/decompressor library

http://google.github.io/snappy/

Softflowd is flow-based network traffic analyser with export

http://www.mindrot.org/softflowd.html

Traps spammers with a very slow smtp-login and return 4xx error

http://freebsdspamd.sourceforge.net/

Spawns fastcgi applications

http://redmine.lighttpd.net/projects/spawn-fcgi

Voice communication over data networks

http://speak-freely.sourceforge.net/

open-source patent-free voice codec

http://www.speex.org/

Sphinx Full-Text Search Engine

http://sphinxsearch.com/

Sphinx Full-Text Search Engine

http://www.sphinxsearch.com/

A standalone JavaScript interpreter from the Mozilla project

http://www.mozilla.org/js/spidermonkey/

Tool for statically checking sourcecode for security vulnerabilities

http://www.splint.org/

SQL database engine in a C library

https://www.sqlite3.org/

HTTP Caching Proxy

http://www.squid-cache.org/

State Threads Library for Internet Applications

http://state-threads.sourceforge.net/

Library that supports startup notification spec from freedesktop.org

https://www.freedesktop.org/wiki/Software/startup-notification/

Advanced IP/IPv6 subnet calculation and discovery

http://www.seccuris.com

Version control system

http://subversion.apache.org/

Allow others to run commands as root

https://www.sudo.ws/

Low level console graphics library

http://www.svgalib.org/

Mouse and keyboard sharing utility

https://symless.com/synergy

Network tool designed for high performance and accurate monitoring

http://puck.nether.net/sysmon/

Type 1 font rasterization library for Unix/X11

https://www.t1lib.org/

Six utilities for manipulating t1 fonts

https://www.lcdf.org/~eddietwo/type/

Library for manipulating ID3 tags and Ogg comments

http://taglib.github.com/

Hierarchical pool based memory allocator

https://talloc.samba.org/