Interesting blog, found via the link to https://www.openbsd.org/papers/bsdcan-signify.html on https://blog.vyos.io/minisign-the-future-of-vyos-image-signature-verification
Examples are
signify - sign and verify https://flak.tedunangst.com/post/signify
humungus a mercurial server/web interface written in Go, https://humungus.tedunangst.com/r/humungus and https://flak.tedunangst.com/post/humungus
X11 example programs such as timescroll - remap ctrl-scroll to undo and redo, https://humungus.tedunangst.com/r/xtoys

A small collection of tools for the X Window System. Found on https://wiki.xxiivv.com/site/catclock.html

Found on https://groups.google.com/g/plan9port-dev/c/KD9Bh9RryW8/m/SuYpW1--BAAJ

This document describes how to configure Xorg XKB from a user's point of view. It covers basic configuration syntax and gives also a few examples.
See also the "X Keyboard Configuration Database" https://www.freedesktop.org/wiki/Software/XKeyboardConfig and
"Custom Keyboard in Linux/X11" http://people.uleth.ca/~daniel.odonnell/Blog/custom-keyboard-in-linuxx11 on Daniel Paul O'Donnell's blog.

Found via https://pirsquared.org/blog/, where I followed a link to the sad, but interesting story of the Xfree fork to X.org.
http://asterisk.dynevor.org/xfree-forked.html
I have not read
https://matthew-brett.github.io/curious-git/
yet, but it sounds interesting.

Interesting software, such as
unifdef selectively removes C preprocessor conditionals. My version of this program now shipped by all the BSDs (including Mac OS X) and is used by the Linux kernel build system.
regpg safely stores server secrets using gpg, so you can keep them in version control.
picoro - tiny coroutine implementations in pure C. I wrote an accompanying article, coroutines in 20 lines of standard C.
Counting the days - tiny routines for converting Gregorian dates into linear counts, like Julian day numbers or Unix time_t. The date of the count - a small routine for converting linear day counts into Gregorian dates.
https://dotat.at/@/2016-04-22-synergy-vs-xmodmap-fight.html Why you can't use xmodmap to change how Synergy handles modifier keys
His log of links, https://dotat.at/:/ which I found on the TUHS mailing list is also worth reading. He explains a bit about this log on http://dotat.at/.

Xpra is an open-source multi-platform persistent remote display server and client for forwarding applications and desktop screens.
It gives you remote access to individual applications or full desktops.
On X11, it is also known as screen for X11: it allows you to run programs, usually on a remote host, direct their display to your local machine, and then to disconnect from these programs and reconnect from the same or another machine, without losing any state.
It can also be used to forward full desktops, from X11 servers, MS Windows, or Mac OS X.

Xpra also allows forwarding of sound, clipboard and printing services.
Sessions can be accessed over SSH, or password protected over plain TCP sockets with or without SSL.
Xpra is usable over reasonably slow links and does its best to adapt to changing network bandwidth constraints.

Blog article about using the simulated keys of the Emacs X Window Manager (EXWM) to change keymaps of programs such as Mozilla Firefox.

xpra or X Persistent Remote Applications is a tool which runs X clients, typically on a remote host, and directs their display to the local machine without losing any state.

How to set up keyboard bindings to Unicode characters in X11.