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/

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

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

SixXS IPv6 TIC+ tunnel broker heartbeat client

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

Graphical login manager for X11, derived from Login.app

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

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

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

Open-source audio processing library

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

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

Common interface to speech synthesis

https://devel.freebsoft.org/speechd

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/

Standalone JavaScript based from Mozilla 17-esr

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

SpiderOak Client (Linux version)

https://spideroak.com/

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/

Webmail system which accesses mail over IMAP

http://www.squirrelmail.org/

Protect hosts from brute-force attacks against SSH and other services

https://www.sshguard.net/

Protect hosts from brute force attacks against ssh and other services using ipfilter

http://sshguard.sourceforge.net

Protect hosts from brute force attacks against ssh using ipfw

http://sshguard.sourceforge.net

Protect hosts from brute force attacks against ssh using pf

http://sshguard.sourceforge.net

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

Allow others to run commands as root

https://www.sudo.ws/

Low level console graphics library

http://www.svgalib.org/

Simplified Wrapper and Interface Generator

http://www.swig.org/

Generate wrappers for calling C/C++ code from other languages

http://www.swig.org/

Mouse and keyboard sharing utility

https://symless.com/synergy

Helps to install application configuration files

http://www.Courier-MTA.org/sysconftool/

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/

Online encrypted backup service (client)

http://www.tarsnap.com/

Tool Command Language

http://www.tcl.tk/

Shell wrapper for tclsh (Tcl)

Tool Command Language

http://www.tcl.tk/

Tool Command Language

http://www.tcl.tk/