EBML (Extensible Binary Meta Language), sort of binary version of XML

https://www.matroska.org/

Collection of C++/Qt classes designed to use the APIs of The Echo Nest

https://github.com/lfranchi/libechonest

Command line editor library

http://thrysoee.dk/editline/

Library for Emulated Input

https://gitlab.freedesktop.org/libinput/libei

Public ELF file access library similar to libelf(3) in Solaris

https://web.archive.org/web/20181111033959/www.mr511.de/software/english.html

Enhanced Metafile Library

http://libemf.sourceforge.net/

Small epoll implementation using kqueue

https://github.com/jiixyj/epoll-shim

Library to handle OpenGL function pointer management

https://github.com/anholt/libepoxy

Library for generating documents in ePub format

http://libepubgen.sourceforge.net/

Liberation fonts from Red Hat to replace MS TTF fonts

https://github.com/liberationfonts/liberation-fonts

Library for some string essentials

https://libestr.adiscon.com/

Mail framework for C language

http://www.etpan.org/libetpan.html

Full-featured and high-performance event loop library

http://software.schmorp.de/pkg/libev.html

Linux Event Device library

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

API for executing callback functions on events or timeouts

https://libevent.org/

Library for inspecting program's backtrace

http://www.gnu.org/software/libc/manual/html_node/Backtraces.html

Library to read digital camera file meta-data

https://libexif.github.io/

Application library for the Xfce desktop environment

https://www.xfce.org/

Language guessing by N-Gram-Based Text Categorization

https://wiki.documentfoundation.org/Libexttextcat

Video encoding library

http://fame.sourceforge.net/

Fork of json-c (JSON implementation in C)

https://github.com/rsyslog/libfastjson

Foreign Function Interface

https://sourceware.org/libffi/

Provides library functionality for FIDO 2.0

https://developers.yubico.com/libfido2/

C++ library for building platform-independent programs

https://lib.filezilla-project.org/

Core library of PCManFM file manager

https://wiki.lxde.org/en/Libfm

LibFM-Extra library

https://wiki.lxde.org/en/Libfm

Formatting library for C++

https://fmt.dev/

The fontenc Library

https://www.x.org/

Library routines for working with Flashpix images

https://www.i3a.org/

Library and tools to access the Apple File System (APFS)

https://github.com/libyal/libfsapfs

Library and tools to access the Extended File System

https://github.com/libyal/libfsext

Library and tools to access the File Allocation Table File System

https://github.com/libyal/libfsfat

Library and tools to access the Mac OS Hierarchical File System (HFS)

https://github.com/libyal/libfshfs

Library and tools to access the New Technology File System (NTFS)

https://github.com/libyal/libfsntfs

Library and tools to access the SGI X File System

https://github.com/libyal/libfsxfs

Library (using libusb) to talk to FTDI chips

http://www.intra2net.com/de/produkte/opensource/ftdi/

Library for Windows NT data types

https://github.com/libyal/libfwnt

General purpose crypto library based on code used in GnuPG

https://www.gnupg.org/software/libgcrypt/index.html

Provides uniform access to different kinds of data sources

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

Provides Berkeley DB backend for the libgda5 library

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

Provides Java DB Connector backend for the libgda5 library

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

Provides ldap access for the libgda5 library

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

Provides mdb backend for the libgda5 library

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

Provides postgresql access for the libgda5 library

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

The libgda 5 ui library

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

GLib based implimentation of the GData protocol

http://live.gnome.org/libgdata

GDI+ API for System.Windows.Forms in Mono

https://www.mono-project.com/docs/gui/libgdiplus/

GObject collection library

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

Library for reading and writing GeoTIFF information tags

https://github.com/OSGeo/libgeotiff

GObject based library for handling and rendering epub documents

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