GNOME application for managing encryption keys (PGP, SSH)

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

Minimal seat management daemon and universal library

https://git.sr.ht/~kennylevinsen/seatd

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

GLSL/HLSL to SPIR-V shader compiler

https://github.com/google/shaderc

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

Pack, send, and unpack shell archives; synchronize via e-mail

https://www.gnu.org/s/sharutils/

Generic script compiler

https://github.com/neurobin/shc/

Benchmark utility for POSIX shell comparison

https://github.com/shellspec/shellbench

Listen to internet radio

https://gitlab.gnome.org/World/Shortwave

Font dumper for the X font server

https://www.x.org/

HTTP regression testing and benchmarking utility

https://www.joedog.org/JoeDog/Sieg

MacOS High Sierra like theme for GTK 3, GTK 2 and Gnome-Shell etc

https://github.com/vinceliuice/Sierra-gtk-theme

Sigar system information API

https://support.hyperic.com/display/SIGAR/Home

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

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

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

General purpose C libraries used by skarnet.org software

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

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

https://contents.meetbsd.ir/apps/opensource/slim/

SLang-based newsreader

https://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

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

Session Manager Proxy

Fast compressor/decompressor library

https://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

https://www.snort.org/

Snowball stemmer library for C

https://snowballstem.org/

Flow-based network traffic analyzer and exporter

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

Platform for continuous inspection of code quality

http://www.sonarqube.org/