QMK (Quantum Mechanical Keyboard) is an open source community centered around developing computer input devices. The community encompasses all sorts of input devices, such as keyboards, mice, and MIDI devices. A core group of collaborators maintains QMK Firmware, QMK Configurator, QMK Toolbox, qmk.fm, and this documentation with the help of community members like you.
See also https://github.com/mihaiolteanu/mugur, an Emacs program to help configuring a QMK keyboard.

Small. Sloccount counts under 2000 lines of code, small enough to allow audits. The binaries can be under 50KB, small enough for many embedded targets.
Easy to deploy. Just add monocypher.c and monocypher.h to your project. They compile as C99 or C++ and are dedicated to the public domain (CC0-1.0, alternatively 2-clause BSD).
Portable. There are no dependencies, not even on libc.
Honest. The API is small, consistent, and cannot fail on correct input.
Direct. The abstractions are minimal. A developer with experience in applied cryptography can be productive in minutes.
Fast. The primitives are fast to begin with, and performance wasn't needlessly sacrificed. Monocypher holds up pretty well against Libsodium, despite being closer in size to TweetNaCl. (More detailed benchmark)

Successor of Dave Love's http://www.loveshack.ukfsn.org/emacs/multi-mode.el, found via
https://github.com/jingtaozf/literate-lisp

Mentioned on the TUHS mailing list https://minnie.tuhs.org/pipermail/tuhs/2021-February/023182.html

Uses Elixir.

Settings for emerge, smerge sounds interesting too.

This repository provides a tiny .emacs file to set up Emacs quickly for Common Lisp programming. README.md provides a detailed description of how to set it up and get started with Common Lisp programming.

Instead of trying to create a single, static firmware, OpenWrt provides a fully writable filesystem with package management. This frees you from the application selection and configuration provided by the vendor and allows you to customize the device through the use of packages to suit any application. For developers, OpenWrt is the framework to build an application without having to build a complete firmware around it; for users this means the ability for full customization, to use the device in ways never envisioned.

Pikchr (pronounced "picture") is a PIC-like markup language for diagrams in technical documentation. Pikchr is designed to be embedded in fenced code blocks of Markdown or similar mechanisms of other documentation markup languages.
Pikchr source code is released under a zero-clause BSD license.

This suite of open source tools is the software development platform you've been waiting for. We've taken the wisdom of the most successful open-source communities and turned it into a platform of efficient engineering tools.

Absolutely no tracking or advertising
All features work without JavaScript
The fastest, most lightweight software forge
100% free and open source software
Sourcehut is currently (2020-09) available as a public alpha.
Note that it includes a Plan9(front) continuous integration service
https://sourcehut.org/blog/2020-05-11-sourcehut-plus-plan-9/

Recommended by Brett Gilio
https://brettgilio.com/posts/2020-10-01-why-self-host.html

David Rosenthal's blog. Other interesting articles include
https://blog.dshr.org/2020/05/the-death-of-corporate-research-labs.html
https://blog.dshr.org/2020/06/informational-capitalism.html
https://blog.dshr.org/2020/03/more-on-failures-from-fast-2020.html