Collectively, people have spent more time in Garry's Mod than the human civilization exists.
Some people say, Garry's Mod was the reason why so many people are into 3D modeling these days, others claim that Garry's Mod is only suitable for those who want to make a funny YouTube video, but one thing is certain, this game has been a cultural phenomenon that helped shape the game industry and is still popular even now, 15 years after its release.
It's been revealed recently how popular Garry's Mod really is by the development team Facepunch Studios, the studio that created Garry's Mod and Rust. It turned out, Garry's Mod has been bought twice as often as Hald-Life 2 with more than 20 million sales. Out of these 20 million, 11 million spent more than 10 hours in-game, and more than 3 million people spent 100+ hours creating scenes, games, and YouTube videos in Garry's Mod.
Collectively, people have spent more than 253.000 years in this game.