Source Engine is a very decent one, I think, but for some reason it doesn’t seem to be any popular among independent developers. The most of them use Unity, many use Unreal Engine. However, it surprises me: Source Engine “hosts” many iconic games, such as Half-Life, Counter-Strike, Portal. Also, it has very decent physics, and Half-Life: Alyx shows that this engine is capable in portraying characters realistically enough - though I’m not sure how well it works with car physics. So anyway, why is that engine seems to be ignored by many independent developers - or maybe, I’m just not aware of many great games working on Source Engine?