I spend a considerable amount of time every day playing this IO games. I believe they are really fun to play as they are easy to understand and they are online. It is really a great fun to play games with your friends without the need of downloading and installing some additional software. You just need a modern browser.
Also there are a lot of options. Which a good thing because there is always something that you are going to love. If you are bored just open your browser and visit IO Games Network and start playing a game. It is that simple.
There are many variants, I prefer to play on iospace.games/ the most popular games here are Slither.io, Agar.io, Starve.io and many others. You can also find some other games like Deeeep.io, Mope.io, Moomoo.io, Foes.io, Lordz.io and so on.