Battle royale
A hundred players, a shrinking map, one survivor — the genre that went from mod to the industry's most copied format in three years.
The form grew out of mods for the military simulator ARMA, where Brendan Greene built a variant with randomised equipment and a zone that contracts and forces encounters. The idea became a standalone game with PUBG in 2017, and the same year Epic added a battle royale mode to Fortnite that quickly became bigger than everything else.
The genre also carries a business model. The games are free and make money on cosmetics and season passes, which makes the player count both product and marketing. The format has since been copied into nearly every major shooter series.