Roblox was pretty interesting in that it has this built in game editor that is very accessible, but is also highly extensible through Lua so the players/builders can ramp up their skills over time.

Add to that it's marketplace. Many users will never using the building tools and just play games made by other players. Not entirely unique, I was doing Unreal mods decades ago, but the way it is all presented and the varying levels of accessibility are still compelling.