Agar.io

Agar.io is a 2D massively multiplayer io game published by Miniclip and released on April 28, 2015. It is available to play in a browser with the URL agar.io, as well as a mobile application available for iOS and Android devices.

Gameplay
In this game, the player controls a circular cell where the objective is to eat smaller cells and pellets to become a bigger cell, and the bigger cell, the higher the score is.