Wings.io is a 2D battle game that is conducted in the sky. In this game, you fly around your aircraft in the sky and gather crates of weapons, as well as consuming the flourescent balls. The main point of the game is to draw your guns and shoot every other enemy.
germs.io is a 2D single player war game in which you shoot certain substances to your opponents and gather food to get bigger. germs.io
Agario abs0rb.me is an extremely simple 2D action game in which you have complete control over a ball.
You can play Hole.io unblocked at a99.io.
Agar Wtf is a widely popular 2D online action game. In this game, players command a cell which looks like a ball.