This is a prototype for the upper (second) stage of spacex's next-gen rocket [1] they are developing that uses their new full-flow staged combustion raptor engine [2]. This is the ship they plan to use for upcoming mars, moon, etc. missions that will basically replace all other spacex rockets as soon as they can figure out how to get it operating. This prototype is missing the nosecone, control surfaces, and other details, but has the most important parts - engines (one instead of 6 like it will eventually have) and fuel+oxidizer tanks.

[1] https://en.wikipedia.org/wiki/SpaceX_Starship

[2] https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-f...