Slither.io

Slither.io is free for all battle arena type game and definitely one of the more popular io games around currently; here you play as a snake in an agar.io like world and try to gain size whilst taking out other player-controlled snakes. Around the map are tons of small food orbs to collect which will slowly but surely increase your snakes size, you can also gain size quicker by consuming an enemy snake. The objective of this game is ultimately survival but some of the more competitive snakes also aim to be the biggest and baddest mother trucker out there by reaching a top spot on the leader board.