Universal configuration library parser

https://github.com/vstakhov/libucl

libudev-compatible interface for devd

https://github.com/FreeBSDDesktop/libudev-devd

Library to manipulate storage devices, from udisks

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

Library for manipulating Unicode characters and strings

http://www.gnome.org/

Library of Unicode annotation data

http://libuninameslist.sourceforge.net/

Library for converting Unicode strings to numbers

http://billposer.org/Software/libuninum.html

Library for single instance applications

http://live.gnome.org/LibUnique

Unicode string library

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

Library to work with RAR archivies

http://www.rarsoft.com/

Generic stack unwinding library

http://www.nongnu.org/libunwind/

Userspace read-copy-update (RCU) data synchronization library

http://lttng.org/urcu

Communication interface library for usbmuxd

http://marcansoft.com/blog/iphonelinux/usbmuxd

The uTorrent Transport Protocol library and sample utilities

https://github.com/bittorrent/libutp

Multi-platform support library with a focus on asynchronous I/O

https://github.com/libuv/libuv

Video4Linux library

http://freshmeat.net/projects/libv4l

VAAPI wrapper and dummy driver

http://freedesktop.org/wiki/Software/vaapi

VAAPI wrapper for GLX

https://github.com/intel/libva

VDPAU wrapper and tracing library

http://freedesktop.org/wiki/Software/VDPAU

Toolkit to interact with virtualization capabilities

https://libvirt.org/

Glib bindings for Libvirt virtualization API

http://www.libvirt.org

Library and tools for parsing the visio file format structure

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

Abstraction library that sits between apps and visual plugin

http://libvisual.sourceforge.net/

Provide an easy API to write one's own vnc server

http://libvncserver.sourceforge.net/

Library to provide file system type information

Audio compression codec library

https://www.xiph.org/vorbis/

VP8/VP9 Codec SDK

http://www.webmproject.org/

Adds tablet support to libinput

http://linuxwacom.sourceforge.net/wiki/index.php/Libwacom

String internment library

http://www.netsurf-browser.org/projects/libwapcaplet/

Tools and library for converting Microsoft WMF (windows metafile)

http://wvware.sourceforge.net/libwmf.html

Tools and library for converting Microsoft WMF (windows metafile)

http://wvware.sourceforge.net/libwmf.html

Library used for writing pagers and taskslists

http://www.gnome.org/

Library used for writing pagers and taskslists

http://www.gnome.org/

Tools for importing and exporting WordPerfect(tm) documents

http://libwpd.sourceforge.net/

Tools for importing and exporting WordPerfect(tm) documents

http://libwpd.sourceforge.net/

General-purpose library for WPE WebKit

https://wpewebkit.org/releases

Library and tools to work with WordPerfect Graphics (WPG) files

https://libwpg.sourceforge.net/

Window Maker raster graphics library

http://www.windowmaker.org/

The W3C Reference Library

http://www.w3.org/Library/

Library for encoding H.264/MPEG-4 AVC video

http://www.videolan.org/x264.html

The X protocol C-language Binding (XCB) library

http://xcb.freedesktop.org/

Calculate VESA CVT mode lines

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

Implementation of the XDG Base Directory specification

http://n.ethz.ch/student/nevillm/download/libxdg-basedir/

Widgets library for the Xfce desktop environment

http://www.xfce.org/

Extension library for the Xfce desktop environment

http://www.xfce.org/

Libraries for xine multimedia player

http://www.xine-project.org/

Keymap handling library for toolkits and window systems

http://xkbcommon.org/

XKB file library

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

Utility library to make XKB stuff easier

http://gswitchit.sourceforge.net/

XML API for C++

http://libxmlplusplus.sourceforge.net/

XML parser library for GNOME

http://xmlsoft.org/