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/

GNOME application for managing encryption keys (PGP, SSH)

https://wiki.gnome.org/Apps/Seahorse

Checks installed packages for vulnerabilities

http://github.com/laffer1/security-advisory-client/

Extensive german HTML reference

http://www.selfhtml.org/

Reliable, highly configurable mail transfer agent with utilities

https://www.sendmail.org/

Perl-script to send xmpp (jabber) messages

https://sendxmpp.hostname.sk/

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

Set of utilities that send SCSI commands to devices

http://sg.danny.cz/sg/sg3_utils.html

Fonts from the SGI ProPack 1.4 (originally for Linux)

http://oss.sgi.com/projects/sgi_propack/

Generates groff and HTML from linuxdoc and docbook SGML documents

SGML parser

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/

Collection of shareware ATM fonts from the CICA archives

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/

Font engine for complex non-Roman writing systems

http://silgraphite.sourceforge.net/

simple calendar and agenda application

http://wiki.gnustep.org/index.php/SimpleAgenda.app

Small (150k), fast, perl-based IRC client

http://www.iagora.com/~espel/sirc.html

Fully automated, active web application security reconnaissance tool

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

Slack client for your terminal

https://github.com/erroneousboat/slack-term

Simple facade or abstraction for various logging frameworks

https://www.slf4j.org/

Graphical login manager for X11, derived from Login.app

https://sourceforge.net/projects/slim.berlios/

Theme pack for SLiM login app

http://slim.berlios.de/themes01.php

SLang-based newsreader

http://slrn.sourceforge.net/

Simple Linux Utility for Resource Management

https://slurm.schedmd.com/

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/

Fast compressor/decompressor library

https://github.com/xerial/snappy-java

Small audio and MIDI framework from the OpenBSD project

http://www.sndio.org/

Super Nintendo Entertainment System(SNES) Emulator

http://www.snes9x.com/

Lightweight network intrusion detection system

http://www.snort.org/

Softflowd is flow-based network traffic analyser with export

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

Elegant music player for MPD

http://sonata.berlios.de/index.html

Clean, mean and lean CD ripper for GNOME

http://www.burtonini.com/blog/computers/sound-juicer/

Open-source audio processing library

http://www.surina.net/soundtouch/

Set of fonts by Adobe designed for coders

https://github.com/adobe-fonts/source-code-pro

Set of fonts by Adobe designed for user interfaces

https://github.com/adobe-fonts/source-sans-pro

Set of fonts by Adobe designed for UI

https://github.com/adobe-fonts/source-serif-pro

Custom rulesets for SpamAssassin

http://wiki.apache.org/spamassassin/CustomRulesets