Updated October 28, 2020: New entries added 

You've more than likely played an .io game, or at least seen one being played. But what exactly is the .io genre?

Like most hit mobile game genres, it can be traced back to a single game. Brazilian developer Matheus Valadares's Agar.io was so-named because of its .io domain name, but it kicked off a particular strain of multiplayer game.

Today we find that an .io game is a simplified massively multiplayer online game, typically with an 'everyone for themselves' focus. You don't generally get flashy graphics with an .io game, and they're generally playable on a wide range of modestly specced devices.

Basically, the genre is custom made to create viral gaming moments.

These days, there are hundreds of games out there following the Agar.io template, and plenty that have begun to branch out into new areas.

What follows is a snapshot of a vibrant .io scene. If you're hankering for some massively multiplayer pick-up-and-play goodness, check out some of these games.