Raspbian is the only official Operating System supported by Raspberry Pi. It is based on GUI/Linux system. Download the latest Raspbian image here.
Image with desktop based on Debian Stretch
Raspbian Stretch Lite
Minimal image based on Debian Stretch
This smaller Raspbian OS version is more preferable for the tiny yet powerful circuit boards like Raspberry Pi Zero and Raspberry Pi A+. It is better and upgraded version than raspbian jessie lite.