X Render extension library

http://www.freedesktop.org/Software/xlibs

X Resource usage library

http://www.freedesktop.org/Software/xlibs

X Toolkit library

https://www.freedesktop.org/wiki/Software/xlibs/

X Test extension

http://www.freedesktop.org/Software/xorg

X Video Extension library

http://www.freedesktop.org/Software/xlibs

X Video Extension Motion Compensation library

https://www.freedesktop.org/wiki/Software/xlibs/

X DGA Extension

http://www.freedesktop.org/Software/xorg

X Vidmode Extension

http://www.freedesktop.org/Software/xorg

Free library for decoding ATSC A/52 streams, aka AC-3

http://liba52.sourceforge.net/

Advanced Access Content System implementation

http://www.videolan.org/developers/libaacs.html

Accounts and SSO framework for Linux and POSIX based platforms

https://gitlab.com/accounts-sso

Qt5 wrapper for SSO framework

https://gitlab.com/accounts-sso

WHATWG-compliant and fast URL parser

https://ada-url.com/

Building blocks for modern GNOME applications

https://www.gtk.org/

Adaptive entropy coding library

https://gitlab.dkrz.de/k202009/libaec https://github.com/MathisRosenhauer/libaec

3GPP Adaptive Multi-Rate - Wideband (AMR-WB) Speech Codec

http://www.penguin.cz/~utx/amr

Portable audio output library

https://www.xiph.org/ao/

KSNI App Indicator library

https://launchpad.net/libappindicator

Generic Apache2 Request Library

https://metacpan.org/dist/libapreq2

Tiny C decompression library for several popular compression formats

http://www.onicos.com/staff/iz/release/

Library to create and read several streaming archive formats

https://libarchive.org/

Communication library between internal components for Ultimaker

https://github.com/Ultimaker/libArcus

Memory hard password hashing program and library

https://github.com/P-H-C/phc-winner-argon2

Library for high-performance 2D graphics

http://www.levien.com/libart/

Portable ASS/SSA subtitle renderer

https://github.com/libass/libass

IPC library used by GnuPG and gpgme

http://gnupg.org/related_software/libassuan/index.en.html

Library of assorted spiffy things

Atomic operations access library

https://www.hboehm.info/gc/

Sound library for SGI audio file

http://www.68k.org/~michael/audiofile/

Library for encoding and decoding .avif files

https://github.com/AOMediaCodec/libavif

Ayatana Application Indicators Shared Library

https://github.com/AyatanaIndicators/libayatana-appindicator

Ayatana Indicators Shared Library

https://github.com/AyatanaIndicators/libayatana-indicator

C library providing BLAKE2b, BLAKE2s, BLAKE2bp, BLAKE2sp

https://blake2.net/

Library for fast Base64 encoding and decoding

http://libb64.sourceforge.net/

Library and tools to access the BitLocker Drive Encryption volumes

https://github.com/libyal/libbde

BD+ System research implementation

http://www.videolan.org/developers/libbdplus.html

Prusa Block & Binary G-code reader/writer/converter

https://github.com/prusa3d/libbgcode

Standard C resolver library

https://www.isc.org/software/libbind

Blu-Ray discs playback library for media players

http://www.videolan.org/developers/libbluray.html

Bauer Stereophonic-to-Binaural DSP

https://bs2b.sourceforge.net/

Libburnia library to read/write optical discs

https://dev.lovelyhq.com/libburnia/web/wikis/home

Graphics library that outputs text instead of pixels

http://caca.zoy.org/

Library to support cross-platform AES encryption

https://github.com/libyal/libcaes

Implementation of the Freedesktop sound theme spec

http://0pointer.de/lennart/projects/libcanberra/

Implementation of the Freedesktop sound theme spec

https://0pointer.de/lennart/projects/libcanberra/

Implementation of the Freedesktop sound theme spec

http://0pointer.de/lennart/projects/libcanberra/

Implementation of the Freedesktop sound theme spec

https://0pointer.de/lennart/projects/libcanberra/

C library implementing the Cangjie input method

https://github.com/Cangjians/libcangjie

CBOR protocol implementation for C and others

https://github.com/PJK/libcbor

Library for collision detection between two convex shapes

https://github.com/danfis/libccd