raspberry pi - OS

https://www.makeuseof.com/tag/7-operating-systems-you-can-run-with-raspberry-pi/

Raspian, Kano,

media center (Kodi)
http://openelec.tv/get-openelec
https://osmc.tv/download/
https://libreelec.tv/downloads/

Game Emulator
RetroPie (game), https://retropie.org.uk/download/
RecalBox, https://www.recalbox.com/diyrecalbox


FreeBSD, https://wiki.freebsd.org/FreeBSD/arm/Raspberry%20Pi

ChromiumOS, https://flintos.io/download/

Android, http://androidpi.wikia.com/wiki/Android_Pi_Wiki