I usually ignore youtube comments but recently I saw a few that mentioned this game and it's kind of addictive. (I once got to #5 on the leaderboard

)
Basically every player around the world is a cell, and there's particles you can eat to grow bigger, but you can also eat smaller cells. (There's also "viruses" and pressing the spacebar to "split", that's a bit more complicated at first but you'll figure it out. Overall the game is really simple but I find it really fun!)
the site is: agar.io
My nickname on it is just "Alex" lol