Cleanjaro is a custom spin of Manjaro, which in turn, is based on the independently developed Arch Linux operating system. Within the Linux community, Arch itself is renowned for being an exceptionally fast, powerful, and lightweight distribution that provides access to the very latest cutting edge and bleeding edge software.
However, Arch is also aimed at more experienced or technically-minded users. As such, it is generally considered to be beyond the reach of those who lack the technical expertise required to use it. Manjaro on the other hand provides all the benefits of the Arch operating system combined with a focus on user-friendliness and accessibility. In recent times though the development direction of Manjaro has become questionable to many.
This is where Cleanjaro comes in. It aims to create a version of Manjaro from yester-year, before questionable development paths started to be followed.