X font library

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

Client-sided font API for X applications

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

X Input extension library

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

X11 Xinerama library

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

X Miscellaneous Utilities libraries

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

X Pixmap library

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

X Present Extension library

https://gitlab.freedesktop.org/xorg/lib/libxpresent

X Resize and Rotate extension library

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

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/

HE-AAC+ Codec as Shared Library

http://tipok.org.ua/node/17/

Advanced Access Content System implementation

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

Building blocks for modern GNOME applications

https://www.gtk.org/

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

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

Portable audio output library

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

Library to create and read several streaming archive formats

https://libarchive.org/

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

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

Atomic operations access library

https://github.com/ivmai/libatomic_ops

Sound library for SGI audio file

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

Library for fast Base64 encoding and decoding

http://libb64.sourceforge.net/

BD+ System research implementation

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

Standard C resolver library

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

Blu-Ray discs playback library for media players

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

Component and compound document system for GNOME2

http://www.gnome.org/

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/

Implementation of the Freedesktop sound theme spec

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

Implementation of the Freedesktop sound theme spec

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

CBOR protocol implementation for C and others

https://github.com/PJK/libcbor

Generic driver for USB CCID and ICCD

https://ccid.apdu.fr/

Library for playing audio CDs

http://libcdaudio.sourceforge.net/

Library to access data on a CDDB server

http://libcddb.sourceforge.net/

Compact Disc Input and Control Library

http://www.gnu.org/software/libcdio/

Read audio from the CDROM directly as data

http://www.gnu.org/software/libcdio/

C library aimed to provide a Gtk+ widget to display rasterized maps and markers

http://projects.gnome.org/libchamplain/

Tool to check shared library links

http://svn.idaemons.org/cgi-bin/viewvc.cgi/trunk/?root=libchk

Ultralightweight JSON parser in ANSI C

https://github.com/DaveGamble/cJSON

Required library functions for OpenCL C programming language

http://libclc.llvm.org/

Alternative configuration system for Compiz

Simple library for manipulating structured configuration files

https://www.hyperrealm.com/libconfig/libconfig.html