Agar.io

In this simple game, which has a squared background just like a maths book, various coloured circles - cells - move around on a map. You control one of these circles.
The aim is to make your circle as big as possible, by collecting small bits of mass which you find scattered around, or by eating other players. However, you're only able to eat them if you're 25 percent bigger then them; if they're 25 percent bigger, of course, they'll eat you.
Before you start the game you can customise the name of your player and if you choose specific names the shape will have a specific appearance - for example, if you type 'mars' then the circle will look like the planet Mars.
Millions of people around the world are playing this game, but if anyone near you is playing they will enter the same server, making it easier to compete with your friends. It's extremely addictive, especially if you end up playing against your mates, and very competitive.
Your mass is listed at the bottom left of your screen; there's a rankings list at the top right, which includes the top 10 players with the biggest mass. If you reach number one you can screenshot and brag about it to your friends, or just carry on playing. Henrique Pedrette