if you mean the map, it's not a mod, it's the test circuit. cant play in it on flatout ultimate carnage, but when you want to select a car in flatout2, just press delete, and you'll get there too:)
I remember watching the Flatout videos few years ago when i was young, where are these times, now the new videos are fake, boring and full of clickbaits
by free roam mod,i mean that he can drive to places,where you usually cant,where the game resets automatically. i know how to get on this track myself.