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/

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

https://www.speex.org/

Tools for processing SPIR-V intermediate shader language modules

https://github.com/KhronosGroup/SPIRV-Tools

Monospaced bitmap fonts for Xorg and vt(4)

https://github.com/fcambus/spleen

Japanese custom font based on Noto Sans and Lato

https://github.com/spoqa/spoqa-han-sans

SQL database engine in a C library (ICU flavor)

https://www.sqlite.org/

New set of tools and libraries to work with SquashFS images

https://infraroot.at/projects/squashfs-tools-ng/

Mount a squashfs archive and treat it like a local file system

https://github.com/vasi/squashfuse

HTTP Caching Proxy

https://www.squid-cache.org/ https://github.com/squid-cache/squid/

Library for serialising LV2 atoms to/from RDF

http://drobilla.net/software/sratom

Secure Reliable Transport (SRT) Protocol

https://www.srtalliance.org/

Tool for computing context triggered piecewise hashes

https://ssdeep-project.github.io/ssdeep/

Chat over SSH

https://github.com/shazow/ssh-chat

Mount remote directories over ssh

https://github.com/libfuse/sshfs

Stb single-file public domain libraries for C/C++

https://github.com/nothings/stb/

Generates C++ and Python from ISO10303 files

https://github.com/stepcode/stepcode/wiki

Monospace font created for the French magazine Etapes

https://raphaelbastide.com/steps-mono

OpenType Unicode fonts for Scientific, Technical, and Math texts

http://www.stixfonts.org/

Receives/sends news to/from localhost via NNTP

https://github.com/lazarus-pkgs/suck

Font for programmers and command line users

https://www.kutilek.de/sudo-font

Set of packages for sparse matrix calculation

https://faculty.cse.tamu.edu/davis/suitesparse.html

Symmetric approximate minimum degree

https://faculty.cse.tamu.edu/davis/suitesparse.html

Permutation to block triangular form

https://faculty.cse.tamu.edu/davis/suitesparse.html

Symmetric approximate minimum degree

https://faculty.cse.tamu.edu/davis/suitesparse.html

Constrained column approximate minimum degree ordering

https://faculty.cse.tamu.edu/davis/suitesparse.html

Sparse CHOLesky MODification package

https://faculty.cse.tamu.edu/davis/suitesparse.html

Column approximate minimum degree ordering algorithm

https://faculty.cse.tamu.edu/davis/suitesparse.html

Concise Sparse Matrix package

https://faculty.cse.tamu.edu/davis/suitesparse.html

Extended version of CSparse

https://faculty.cse.tamu.edu/davis/suitesparse.html

Simple LDL^T factorization

https://faculty.cse.tamu.edu/davis/suitesparse.html

Symmetric approximate minimum degree

https://faculty.cse.tamu.edu/davis/suitesparse.html

Read/write sparse matrices

https://faculty.cse.tamu.edu/davis/suitesparse.html

Sparse Left-looking Integer-Preserving LU Factorization

https://faculty.cse.tamu.edu/davis/suitesparse.html

SystemVerilog 2017 Pre-processor, Parser, Elaborator, etc

https://github.com/chipsalliance/Surelog

C++ header-only parsers for various SVG syntaxes

http://svgpp.org/

SystemVerilog linter

https://github.com/dalance/svlint

SystemVerilog language server

https://github.com/dalance/svls

Scalable AV1 encoder

https://01.org/svt

Scalable HEVC encoder

https://01.org/svt

Scalable VP9 encoder

https://01.org/svt

Steve Harris' huge Collection of LADSPA Plugins

http://www.plugin.org.uk

Lightweight image viewer

https://github.com/muennich/sxiv

SymbiYosys (sby): Front-end for Yosys-based formal verification flows

https://yosyshq.readthedocs.io/projects/sby/en/latest/ https://github.com/YosysHQ/sby/

Mouse and keyboard sharing utility

https://symless.com/synergy

Internal sysctl object to implement an improved sysctlbyname(3)

https://gitlab.com/alfix/sysctlbyname-improved/