Garry's Mod is an enormously influential game. The sandbox mismash of Valve's greatest hits put Facepunch Studios on the map, led to unbelievably popular YouTube series like Skibidi Toilet (which is even getting a movie), and was a pioneer in fan-favourite game modes like Prop Hunt that have since found a new home in other titles like Call of Duty.
After 18 years rotting the brains of three generations, Garry's Mod has become the best-selling exclusive PC game of all-time. It beats out giants like Total War: Warhammer 2, Counter-Strike: Global Offensive (now Counter-Strike 2), Escape from Tarkov, Dota 2, and even World of Warcraft with over 20 million copies sold.
Garry's Mod arrived at just the right time, three years into Steam's history when Valve was in its prime, releasing a slew of still-iconic games like Team Fortress 2, Left 4 Dead, Half-Life 2, and Counter-Strike. All of which were brought together under one roof in Garry's Mod, which itself grew year after year with new modes appealing to all different kinds of players.
If you're into sandbox and want to build things, there's a creative mode; if you prefer challenges...