Like its predecessors agar.io and slither.io, diep.io is a
minimalist 2-D MMO game where you level up by first consuming things scattered around the map, then other players whom you think you can take on. Except this time, instead of
controlling cells or snakes, you control tank (or more precisely, circles with shooty squares attached to them). There is a whole tree of tank types you can level up to have, as well as specific aspects of your tank (bullet
penetration, speed, health regen, etc.) you can level up.
Like its predecessors, Diep.io addictive as fuck. It has 4 game modes, 3 more than either other game.