Replacement for xbiff that handles popup window with mail header

Command line utility for PDF viewers

PostIt (R) messages onto your X11 screen

Utility for printing an X window dump

Property displayer for X

Primitive command line interface to the RandR extension

X server resource database utility

Multi-format document reader

https://github.com/linuxmint/xreader

Refresh all or part of an X screen

Save your screen while you entertain your cat

https://www.jwz.org/xscreensaver/

Save your screen while you entertain your cat (for GNOME users)

https://www.jwz.org/xscreensaver/

Save your screen while you entertain your cat (for GNOME users)

https://www.jwz.org/xscreensaver/

WindowMaker dockapp to control XScreenSaver

https://xscreensaverapp.sourceforge.net/

Access X11 selection buffer from command line

http://BSDforge.com/projects/x11/xsel/

Access X selection from command line

http://www.vergenet.net/~conrad/software/xsel/

User preference utility for X

Root window parameter setting utility for X

X Session Manager

Mono based web server

https://www.mono-project.com/

Utility for monitoring keystrokes on remote X servers

http://www.acm.vt.edu/~jmaxwell/programs/xspy/xspy.html

Watches the growth of files or directories

https://www.unicom.com/sw/xtail/

Terminal emulator for the X Window System

https://invisible-island.net/xterm/

Outputs X window titles

https://github.com/baskerville/xtitle

Abstract network code for X

X11 program that displays images of various formats

http://www.trilon.com/xv/

Opensource MPEG-4 codec, based on OpenDivx

http://www.xvid.org/

Video mode tuner for X

Fast and functional image viewer

https://github.com/linuxmint/xviewer

Print out X-Video extension adaptor information

X11 server as Wayland Client

https://wayland.freedesktop.org/xserver.html

Dump an image of an X window

Window information utility for X

Image displayer for X

Extremely fast non-cryptographic hash algorithm

https://xxhash.com/ https://github.com/Cyan4973/xxHash

XKB keyboard layout indicator and switcher

https://sourceforge.net/projects/xxkb/

Magnify, rotate, mirror the image on the X screen

Yet another Basic for Unix and Windows

http://www.yabasic.de/

Display GNOME dialogs from the command line

https://github.com/v1cont/yad

Yet another FTP client, similar to ftp(1)

https://github.com/sebastinas/yafc

Yet Another File Integrity Checker, similar to Tripwire

http://philosophysw.com/software/yafic/

Portable JSON parsing and serialization library in ANSI C

http://lloyd.github.com/yajl/

Enhanced execution box with regex pattern matching

http://offog.org/code/

Complete rewrite of the NASM assembler

https://yasm.tortall.net/

General-purpose console screen reader

https://yasr.sourceforge.net/

Z39.50/SR client and API library

https://www.indexdata.com/resources/software/yaz/

Diff readability enhancher for color terminals

https://github.com/ymattw/ydiff

Terminal wrapper for creating drop-down consoles

http://phrat.de/yeahtools.html

Help browser for the GNOME desktop

https://www.gnome.org/

Utilities to help manage documentation for Yelp and the web

https://wiki.gnome.org/Apps/Yelp/Tools

DocBook XSLT stylesheets for yelp

https://www.gnome.org/