Agar.io is described as «Play online with players around the world as you try to become the biggest cell of them all!» and is a very popular Absorb Game in the games category. There are more than 50 games similar to Agar.io for a variety of platforms, including Online / Web-based, Android, iPhone, iPad and Windows. The best alternative is Nebulous, which is free. Other Agar.io like games are Slither.io, Gota.io, Osmos and Diep.io.Agar.io alternatives are mainly Absorb Games but may also be Survival Games or Crafting Games. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of Agar.io.
