Raspbian and Noobs are currently the two officially-recognized operating systems for the Raspberry Pi single board computer; they both provide a visual front end to your Raspberry Pi hijinks.
Raspbian just got an upgrade, known as PIXEL, adding some (mostly visual) bells and whistles to the original product. It looks like Raspberry Pi users are a bit divided on this at first, since the little computer was originally intended as a learning environment, with simplicity being a main goal.
Some say the new PIXEL OS is bloating things unnecessarily, while others welcome the snazzification and polish.
|A typical Raspberry Pi computer|