Agar.io is based on the beginning of Spore, but now as online multiplayer. You eat smaller cells, until someone finds you a tasty smaller cell. Agar.io is a free online multi-player browser game.
I tried Agar or Agario if you like, and it really caught me. Even though the concept is really simple, it is addiction as nothing else. You control a cell with a mass, and you compete against others to become the biggest cell. It’s pure survival of the fittest. You grow by eating smaller cells, but that is the same for other players, who are trying to eat you.
The game is really well balanced, as the speed of a cell decreases as the mass increases. Also every cell slowly shrinks, if it doesn’t eat, and it does so faster and faster the bigger the cell is. The map also has viruses, that you can use to attack and split bigger cells, so no one is ever safe no matter the size.
Besides playing every man for himself, you can also play as teams, which could great if you where playing 10-20 people in the same room, but lacks the strategic cooperative element, as you cannot communicate. This game type especially sucks, since you cannot choose to play with your friends, but are teamed up with random people.
A chat function is also a feature you miss while playing alone as well. You want to rage and flame when being eating, and compliment others for playing smart.
A nice touch to the game is the skins you can choose from. But there should be a user interface where you could choose, instead of having to guess them and type in random nicknames.