Simfphys and LFS bases. Both made by a talented developer that give new options for both ground and air vehicles.
I've been creating vehicle mods for both these bases (not dupes lmao) for a long while now and I can say I prefer this so much more than the wacky physics that are found with normal Source Engine vehicles and SCars. WAC aircraft is pretty decent as well but I like the simplicity of LFS a lot too.
I wouldn't have 3k+ hours logged in gmod if it weren't for those two addons