Re: https://firmwaresecurity.com/2015/08/28/new-efi-based-operating-systems/
Below is a list of currently-actively “UEFI hobby operating system”-style projects on Github, defining “active” as updated in last 2 months. Projects which haven’t been updated recently are not listed, but there are a few dozen other projects between above link and below list. Most are barely more than a hello-world bootloader; others are nearly-complete operating systems, some in C a few in Rust, I think one was in C#. List not sorted in any order:
https://github.com/vvaltchev/tilck
https://github.com/Michael-Kelley/RoseOS
https://github.com/GreenteaOS/Tofita
https://github.com/ondralukes/OndrOS
https://github.com/MCJack123/craftos-efi
https://github.com/Totsugekitai/minOSv2
https://github.com/portasynthinca3/neutron
https://github.com/wordandahalf/Stelox
https://github.com/kazuminn/minos
https://github.com/hikalium/liumos
https://github.com/sonjt0705/afwj-uefi
https://github.com/justinian/jsix
https://github.com/VerdureOS/Verdure
https://github.com/bSchnepp/Feral
https://github.com/DylanGTech/PiousOS
https://github.com/Lan-t/MyOsLoader
https://github.com/Ocean-git-hub/EgoisticOS
https://github.com/approvers/minimos
Firmware Security 