Aliased from Raspbian, and Raspberry Pi OS
The Raspberry Pi OS, previously called Raspbian, is a Linux-based operating system used for the Raspberry Pi single board computer (SBC).
The RPi OS is available in a 32 bit version and as a 64 bit OS, the latter available in beta as both a standard and "lite" version since mid 2020:
- https://downloads.raspberrypi.org/raspios_arm64/images/
- https://downloads.raspberrypi.org/raspios_lite_arm64/images/
The latest as of this writing is from 5 March of this year. It's not been officially released but it seems to work fine, though most people won't notice any performance increase it is necessary for the Pi 4 8GB to be able to access the full complement of its memory.