Plan 9 - one version of which is 9front, which says this:
"Multiple installation media are provided for PC, Raspberry Pi, MNT Reform, and QEMU. For PC, burn an .iso file to CD, or dd it directly to USB media. For Raspberry Pi or MNT Reform, dd an .img file directly to sdcard.
The pi.img file can be used for Raspberry Pi 1, 2, and 3. The pi3.img file can be used for Raspberry Pi 3 and 4.
QEMU images are provided in QCOW2 format."