Bubble. Io is a game where as a bubble you want to grow as large as possible. You can do this by consuming water droplets - the tiny blue dots spread across the screen. Water portals in each corner teleport you to other side of the screen ( play in full screen for the best experience). If the opponent is smaller than you then you can eat them - they will try to eat you if they are larger!
Updates: 13/1/21: Opponents added 1/1/21: Release date