.io games

2015–2020: Surge in popularity, Agar.io and Slither.io

Agar.io was announced on 4chan on 27 April, 2015 by Matheus Valadares,^[4] a then 19-year-old Brazilian developer. In the game, players control one or more circular cells in a large map with many players, representing a Petri dish. The goal is to gain as much mass as possible by eating cells and player cells smaller than the player's cell while avoiding larger ones which can eat the player's cells. The game went viral on the free online games site Miniclip, and birthed a wave of new .io titles from around 2016—a new genre of large scale, arena based browser games.^[5][6] Slither.io, a free for all multiplayer game in the Snake genre was created in 2016 by Steven Howse, a self-taught independent developer who was inspired by Agar.io. The game would gain traction in the years following. The basic premise of the game is that 50 players compete to eat colored orbs and grow as large as possible, while destroying other player's snakes.^[7][8]

In mid-2016, more games under the domain were released.^[1][3] Most were simple clones of popular games, released in a top down-format.^[2] Notable games released in this period include Diep.io (another game by Matheus Valadares),^[9] ZombsRoyale.io,^[10] Surviv.io, Shellshock.io,^[11] Hole.io, Snake.io, and Krunker.io.

2021–2024: Popularity decline

.io games became popular during the peak of the COVID-19 pandemic; from 2020 to 2021, because of their easy accessibility on the web.^[12] After 2021, the popularity of .io games had generally declined due to the lack of updates and the rise of traditional mobile and video gaming.^[13]