https://github.com/pkgforge-dev/Anylinux-AppImages
https://github.com/VHSgunzo/sharun
EDIT:
It also hardcodes paths so it doesn’t work on things like NixOS or Guix System out-of-the-box.
Also this take makes no sense, flatpak nor snap work on NixOS or Guix out of the box unless the user installs and configures them with all their dependencies, and that usually includes a reboot to make sure the flatpak exports get added to XDG_DATA_DIRS.
Meanwhile appimage can be made to work out of the box in those systems and for those that don't NixOS offers an FHS wrapper to run them.