Sigrok firmware extraction utilities

https://www.sigrok.org/wiki/Firmware

Secure Internet Live Conferencing (SILC) network toolkit

http://www.silcnet.org/

Simple MTP fuse filesystem driver

https://github.com/phatina/simple-mtpfs

simple calendar and agenda application

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

C++ library providing a simple API to INI-style configuration files

https://github.com/brofield/simpleini

Extremely simple IRC client

http://www.suckless.org/programs/sic.html

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

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

Maintains remote websites, uses FTP or WebDAV to sync up w/ local copy

https://www.manyfish.co.uk/sitecopy/

Japanese input method, library part

Japanese input method, binary part

General purpose C libraries used by skarnet.org software

https://www.skarnet.org/software/skalibs/

The "meta-port" for the SKK Japanese-input software

http://openlab.jp/skk/

SKK dictionary from Wikipedia (Japanese edition)

https://github.com/tokuhirom/jawiki-kana-kanji-dict

Jisyo (dictionary) files for the SKK Japanese-input software

http://openlab.jp/skk/dic.html

CDB jisyo (dictionary) files for the SKK Japanese-input software

http://openlab.jp/skk/dic.html

Jisyo-tools for the SKK Japanese-input software

https://github.com/skk-dev/skktools

SKK-like Japanese input method for X11

http://skkinput2.sourceforge.jp/

SKK-like Japanese input method for X11

https://sourceforge.jp/projects/skkinput3/

Dictionary server for the SKK Japanese-input software

http://openlab.ring.gr.jp/skk/index.html

Japanese warehouse keeper sokoban game

https://apps.kde.org/skladnik/

Slack client for your terminal

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

Tool for checking, and diagnosing DNS zones

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

Superior Lisp Interaction Mode for Emacs

https://common-lisp.net/project/slime/

Low-bandwidth, yet greedy and poisonous HTTP client

http://ha.ckers.org/slowloris/

SLang-based newsreader

http://slrn.sourceforge.net/

Select a region in a Wayland compositor

https://wayland.emersion.fr/slurp/

Multi-layered IRC library

http://smartirc4net.meebey.net/jaws/

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

https://www.smartmontools.org

Samba-LDAP management and support tools

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

Hash Algorithm Benchmarking

https://github.com/gvnn3/smhasher/

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

https://github.com/snes9xgit/snes9x

Lightweight network intrusion detection system

http://www.snort.org/

Snowball stemmer library for C

https://snowballstem.org/

Vendor and platform neutral SDR support library

https://github.com/pothosware/SoapySDR

Multipurpose relay and more

http://www.dest-unreach.org/socat/

Softflowd is flow-based network traffic analyser with export

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

SonarQube Plugin for analysis projects with an Apache Ant

http://docs.sonarqube.org/display/SONAR/Installing+and+Configuring+Ant+SonarQube+Task

Scanner component of SonarQube

https://www.sonarqube.org/

Web-based continuous code inspection tool

https://www.sonarqube.org/

Elegant music player for MPD

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

Lightweight C library for storing RDF data in memory

http://drobilla.net/software/sord/

Clean, mean and lean CD ripper for GNOME

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