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/

Simple Linux Utility for Resource Management

https://slurm.schedmd.com/

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/

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/

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

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/

Platform for continuous inspection of code quality

http://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/

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

C/C++ and Java sources to HTML converter

https://www.gnu.org/software/src-highlite/source-highlight.html

Set of fonts by Adobe designed for user interfaces

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

Set of fonts by Adobe designed for UI

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

Custom rulesets for SpamAssassin

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

Highly efficient mail filter for identifying spam

http://spamassassin.apache.org/

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

http://freebsdspamd.sourceforge.net/

DSP library and software FAX machine

https://www.soft-switch.org/

Extremely memory-efficient hash_map implementation

http://code.google.com/p/google-sparsehash

General Framework for Developing Spatial Indices

https://libspatialindex.org/en/latest/

Spatial Extensions for SQLite

https://www.gaia-gis.it/gaia-sins/

Spawns fastcgi applications

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

Super fast C++ logging library

https://github.com/gabime/spdlog

Common interface to speech synthesis

https://devel.freebsoft.org/speechd

CLI and Go API to test internet speed using speedtest.net

https://github.com/showwin/speedtest-go

open-source patent-free voice codec

http://www.speex.org/

Audio compression format designed for speech

http://www.speex.org/

Sphinx Full-Text Search Engine

http://sphinxsearch.com/

Gtk client and libraries for SPICE remote desktop servers

https://www.spice-space.org/

Simple Protocol for Independent Computing Environments

http://www.spice-space.org

Standalone JavaScript based from Mozilla 102-esr

https://spidermonkey.dev/

Standalone JavaScript based from Mozilla 78-esr

https://spidermonkey.dev/

Standalone JavaScript based from Mozilla 91-esr

https://spidermonkey.dev/