ZFSBootMenu is a bootloader that provides a powerful and flexible discovery, manipulation and booting of Linux on ZFS. Originally inspired by the FreeBSD #bootloader, ZFSBootMenu leverages the features of modern #OpenZFS to allow users to choose among multiple "boot environments" (which may represent different versions of a Linux distribution, earlier snapshots of a common root, or entirely different distributions), manipulate snapshots in a pre-boot environment and, for the adventurous user, even bootstrap a system installation via zfs recv.

In essence, #ZFSBootMenu is a small, self-contained #Linux system that knows how to find other Linux kernels and initramfs images within #ZFS #filesystems. When a suitable kernel and initramfs are identified (either through an automatic process or direct user selection), ZFSBootMenu launches that kernel using the kexec command.

https://docs.zfsbootmenu.org/en/v2.3.x/index.html