please does anyone know about any linux system which can be put onto USB flash disk and boot from there + save data only into RAM?

I tried Tails Home, Wikipedia, SourceForge

and found these another distributions:

Whonix - Home, Wikipedia , SourceForge , Github
Liberté Linux - Home , Wikipedia, SourceForge , Github (vs Tails => lightweight, less programs, can install on hd)
Ipredia OS - Home, Wikipedia, SourceForge

List of Linuxes that run from RAM: https://en.wikipedia.org/wiki/List_of_Linux_distributions_that_run_from_RAM

Tails vs Liberté