Library for interpreting and importing Adobe/Macromedia drawings

https://wiki.documentfoundation.org/DLP/Libraries/libfreehand

Library (using libusb) to talk to FTDI chips

https://www.intra2net.com/en/developer/libftdi/

YAML parser and emitter

https://github.com/pantoniou/libfyaml

Provides uniform access to different kinds of data sources

http://www.gnome-db.org/

GObject collection library

https://wiki.gnome.org/Projects/Libgee

Portable, pure C implementation of the Git core

http://libgit2.github.com/

GL Vendor-Neutral Dispatch library

https://gitlab.freedesktop.org/glvnd/libglvnd

A graphics library for GNOME

GNU Regex Library

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

Library for easy management of RSS/Atom/Pie feeds

https://www.gnome.org/

Extensible i/o abstraction for dealing with structured file formats

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

Implementation of the IETF's Calendaring and Scheduling protocols

https://github.com/libical

ID3 tags library (part of MAD project)

http://mad.sourceforge.net/

Image Quantization Library

https://pngquant.org/lib/

Library to communicate with Apple iOS devices

http://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/

SIMD-accelerated JPEG codec library, provides libTurboJPEG

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

Lightweight KMS plane library

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

Easy to use system logging library

https://www.liblogging.org/

Provides a few data structures and helpful functions

https://github.com/cheusov/libmaa

Libmad library (part of MAD project)

http://mad.sourceforge.net/

MATE keyboard shared library

https://mate-desktop.org/

Mixer library for MATE desktop

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

Library to access online weather information

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

Library for handling media art

https://github.com/GNOME/libmediaart

Modbus library

https://libmodbus.org/

ModPlug mod-like music shared libraries

http://modplug-xmms.sourceforge.net/

API library for interfacing MPD

http://www.musicpd.org/libs/libmpdclient

Library and tools for parsing Microsoft Publisher file format

https://wiki.documentfoundation.org/DLP/Libraries/libmspub

MusicBrainz client library for audio metadata lookup

http://musicbrainz.org/

Brush library from the MyPaint project

http://mypaint.org/

SOFA (Spatially Oriented Format for Acoustics) file reader

https://github.com/hoene/libmysofa

C library for creating IP packets

http://sourceforge.net/projects/libnet-dev/

HTTP/2 C Library

https://nghttp2.org/ https://github.com/nghttp2/nghttp2

HTTP/3 C Library

https://nghttp2.org/nghttp3/ https://github.com/ngtcp2/nghttp3

Implementation of QUIC protocol

https://nghttp2.org/ngtcp2/ https://github.com/ngtcp2/ngtcp2

NetSurf public suffix list handling

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

Number to number name and money text conversion libraries

https://numbertext.org

Replacement Objective-C runtime supporting Obj-C 2 features

Ogg bitstream library

https://www.xiph.org/ogg/

Library which provides a way to read/write CAD (DWG/DXF/DXFB) files

https://trac.osgeo.org/gdal/wiki/DWG_driver

High-level API for encoding .opus files

https://opus-codec.org/

Standalone file import filter library for spreadsheet documents

https://gitlab.com/orcus/orcus

Library for managing OS information for virtualization

https://libosinfo.org/

Library and tools for parsing Aldus/Adobe PageMaker documents

https://wiki.documentfoundation.org/DLP/Libraries/libpagemaker

Eclipse Paho C Client Library for the MQTT Protocol

https://github.com/eclipse/paho.mqtt.c