Video4Linux library

https://linuxtv.org/wiki/index.php/V4l-utils

VAAPI wrapper and dummy driver

https://github.com/intel/libva

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 a custom vnc server

http://libvnc.github.io/

Library to provide file system type information

Audio compression codec library

https://xiph.org/vorbis/

VP8/VP9 reference encoder/decoder

https://www.webmproject.org/

Adds tablet support to libinput

https://github.com/linuxwacom/libwacom/wiki

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

https://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

http://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

3D Xaw (Athena Widget Set) replacement with extended fonts

https://sourceforge.net/projects/sf-xpaint/files/

The X protocol C-language Binding (XCB) library

https://xcb.freedesktop.org/

Calculate VESA CVT mode lines

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

Implementation of the XDG Base Directory specification

https://github.com/devnev/libxdg-basedir/

Widgets library for the Xfce desktop environment

https://www.xfce.org/

Extension library for the Xfce desktop environment

https://www.xfce.org/

Libraries for xine multimedia player

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

Keymap handling library for toolkits and window systems

https://xkbcommon.org/

XKB file library

https://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/

Library to help create and query binary XML blobs

https://github.com/hughsie/libxmlb

Module rendering library for xmp

http://xmp.sourceforge.net/

Shared memory 'SyncFence' synchronization primitive

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

The XSLT C library for GNOME

http://xmlsoft.org/XSLT/

YAML 1.1 parser and emitter written in C

https://pyyaml.org/wiki/LibYAML

Library for decrypting and parsing YubiKey One-Time Passwords

https://developers.yubico.com/yubico-c/

GLib/GObject wrapper for the Skydrive and Hotmail API

https://github.com/GNOME/libzapojit

C library for reading, creating, and modifying ZIP archives

https://libzip.org/

ZeroMQ core library (Version 4)

https://www.zeromq.org/

C client interface to Zookeeper server

https://zookeeper.apache.org/

GNU ZRTP library

https://github.com/wernerd/ZRTPCPP

Routines to access raw VBI capture devices

http://zapping.sourceforge.net/doc/libzvbi/

Simple RSS/RDF feed reader

https://lzone.de/liferea/