Uses overlayfs to merge your repository data with that of voidlinux for functioning builds.

Can create a complete repository of signed packages which you could then host yourself.

Making (linux) OS systems immutable using btrfs subvolumes. Gives atomic upgrades, editable-via-overlayfs /etc and retains persistence, but otherwise can turn any os into immutable systems.

Very interesting (created by ChimeraOS team, so presumably used there)