Splix.io

io is an online multplayer game where you have to conquer as much land as possible and become the biggest of them all. You can move your player around using the arrow keys or wasd. If you're in your own area, you're safe, but once you leave your area you'll leave a trail behind, once anyone (including yourself) hits that trail, you die. When you get back to your area, the blocks that you have surrounded will be yours.