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
https://dotat.at/@/2023-05-26-whence-time.html Where does my computer get the time from?
https://dotat.at/@/2023-08-04-unix69.html a neat keyboard map
https://dotat.at/@/2024-01-29-four-point-egg.html construct an egg shape with straightedge and compass
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/.

Enjoy the various programming-themed writings available on offer. The latest post is available below and the archive link is directly above this text.

Milonga is a customizable theme for Emacs, based on the Tango color palette. The specificity of Milonga is in the way it is programmed. Every basic color in the palette has a corresponding foreground and background face, and every themed face inherits from one or two of them instead of having its color hard-wired. This means that if you want to change one of the original colors throughout the theme, you only need to customize one (or two) faces.

Milonga provides the `milonga-theme' Custom group from which you may access the aforementioned core faces.

It offers nearly GNU/Linux Emacs experience in Windows with minimum configuration efforts. A set of additional GNU command-line and development tools is available through the network installer. Includes commonly used POSIX utilities such as diff, grep, aspell.
Optionally, a number of Lisp implementations can be installed.

Collection of short interviews with 14 Lisp programmers.

EISL was written by Kenichi Sasagawa
https://qiita.com/sym_num/items/793adfe118514668e5b0
The license appears to be similar to BSD/MIT to my non-laywer eyes: https://github.com/sasagawa888/eisl/blob/master/license.txt
It provides an interface to WiringPi, allowing control of the GPIO pins on a Raspberry π.

cl-6502 is a Common Lisp emulator, assembler and disassembler for the MOS 6502 processor.

Nim is a systems and applications programming language. Statically typed and compiled, it provides unparalleled performance in an elegant package.

   High-performance garbage-collected language
   Compiles to C, C++ or JavaScript
   Produces dependency-free binaries
   Runs on Windows, macOS, Linux, and more

KISS is aimed to be a conforming ISLisp processor.
The development is at the initial stage.

The current KISS is an interpreter written in C and ISLisp by Yuji Minejima.

See also the public domain draft of the ISlisp specification
https://github.com/nenbutsu/ISLispHyperDraft
https://nenbutsu.github.io/ISLispHyperDraft/islisp-v23.html

Interesting blog about programming, mathematics, Lisp and Plan 9.