I believe(didnt look it up recently) it started as a mod made by someone named garry for half life 2 to make it more like a sandbox game and then it snowballed from there into a fully fledged sandbox game that is often modded heavily. The mods are very supported, you can join a server without installing any mods client side and they will auto download and you can just play, provided you don’t mind missing textures.
I believe(didnt look it up recently) it started as a mod made by someone named garry for half life 2 to make it more like a sandbox game and then it snowballed from there into a fully fledged sandbox game that is often modded heavily. The mods are very supported, you can join a server without installing any mods client side and they will auto download and you can just play, provided you don’t mind missing textures.