Library with GTK+ widgets for mobile phones

https://gitlab.gnome.org/GNOME/libhandy/

ISO/IEC 23008-12:2017 HEIF file format de- and encoder

https://github.com/strukturag/libheif

HTML5 parser library

https://www.netsurf-browser.org/projects/hubbub/

Implementation of the IETF Calendaring and Scheduling protocols

https://github.com/libical

Character set conversion library

https://www.gnu.org/software/libiconv/

ID3 tag manipulation library

https://www.underbit.com/products/mad/ https://codeberg.org/tenacityteam/libid3tag

Internationalized Domain Names command line tool

https://www.gnu.org/software/libidn/

Implementation of IDNA2008 internationalized domain names

https://www.gnu.org/software/libidn/#libidn2 https://gitlab.com/libidn/libidn2

C library that supports plugin printer driver for Ghostscript

https://www.linuxprinting.org/ijs/

Image Quantization Library

https://pngquant.org/lib/

Library to communicate with Apple iOS devices

https://www.libimobiledevice.org

Common code used by the libimobiledevice project

https://www.libimobiledevice.org

Kevent based inotify compatible library

https://github.com/libinotify-kqueue/libinotify-kqueue

Generic input library

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

ODBC 3.x driver manager, for universal data source access

https://www.iodbc.org/

Library for manipulating IPTC metadata stored in image files

https://libiptcdata.sourceforge.net/

Library for Evation's Irman infrared receiver

https://libirman.sourceforge.io/

Libburnia ISO9660 filesystem creation library

https://dev.lovelyhq.com/libburnia/web/wiki/Libisofs

Standalone client/server 9P library

https://libs.suckless.org/deprecated/libixp/

SIMD-accelerated JPEG codec library, provides libTurboJPEG

https://libjpeg-turbo.virtualgl.org/

JPEG XL reference encoder/decoder

https://jpeg.org/jpegxl/

Engine to interpret compiled KMFL keyboard tables

https://kmfl.sourceforge.net/

Reference implementation of OGC KML 2.2

https://github.com/libkml/libkml

Library to make X.509 certificates

https://www.gnupg.org/aegypten2/

Interface library to access tags for identifying languages

http://tagoh.bitbucket.org/liblangtag/

Lightweight KMS plane library

https://gitlab.freedesktop.org/emersion/libliftoff

Lightweight Open Sound Control implementation

https://liblo.sourceforge.net/

Standard lockfile library

https://github.com/miquels/liblockfile

Easy to use system logging library

https://www.liblogging.org/

Easy to use C/C++ seam carving library

https://liblqr.wikidot.com/

Library for manipulating RDF files describing LADSPA plugins

https://github.com/swh/LRDF

System independent dlopen wrapper

https://www.gnu.org/software/libtool/

LZ4 compression library, lossless and very fast

https://lz4.org/ https://github.com/lz4/lz4

Provides a few data structures and helpful functions

https://github.com/cheusov/libmaa

MPEG audio decoder library

https://www.underbit.com/products/mad/ https://codeberg.org/tenacityteam/libmad

MATE keyboard shared library

https://mate-desktop.org/

Mixer library for MATE desktop

https://github.com/mate-desktop/libmatemixer

Library to accessing online weather informations

https://mate-desktop.org/

Extensible Multimedia Container Format

https://www.matroska.org/

Library for the MaxMind DB file format used for GeoIP2

https://github.com/maxmind/libmaxminddb

Multi-cipher cryptographic library (used in PHP)

https://mcrypt.sourceforge.net/

Library for handling media art

https://www.gnome.org/

C library for accessing a memcache cluster

https://people.FreeBSD.org/~seanc/libmemcache/

C/C++ client library and tools for the memcached server

https://awesomized.github.io/libmemcached/ https://github.com/awesomized/libmemcached

Set of utilities to benchmark productivity of system calls

http://hub.opensolaris.org/bin/view/Project+libmicro/

C library for embedding HTTP server functionality

https://www.gnu.org/software/libmicrohttpd/

MikMod Sound Library

https://mikmod.sourceforge.net/

Library providing Sendmail Mail Filter API

http://www.sendmail.com/sm/open_source/milter/

Multiple-image Network Graphics (MNG) reference library

https://www.libmng.com/

Library and tools to access the Mac OS disk image formats

https://github.com/libyal/libmodi