Mope.io – Begin as a mouse, and find berries to eat. Eat from the berry bushes to gain experience points and grow stronger, and drink water to stay hydrated – otherwise you will die of dehydration. But more importantly, watch out for predators who are trying to eat you. As you eat more and more, you will progress up the food chain, and will be able to eat animals that are below you on the food chain. You evolve into a new, more powerful animal every time you gain enough experience, and are able to eat the lower level animals. The more powerful you become, the more players you can attack, and the stronger your character becomes!
Mope.io is a great io game, which you should try out if you like the io games genre.