I have used, compiled, or hacked all of these at one point or another.

ARM devices
  Android, includes instructions on how to root a Samsung Edge S7 SM-G935F
  D-Link DNS-320
  Raspberry Pi

  Windows, includes software you may want
    Bart's PE

    FreeBSD, my favorite OS

    Knoppix Live CD
    Ubuntu 10.x, changed how sound was handled without telling community in their release notes

  System V
    AIX, reported a major bug with the xlc compiler in 99
    Sun Solaris 8, mostly test questions