I've recently heard of Bevy, which is a new FOSS game engine made with Rust! I don't know a lot about it but my gamedev friend is excited about it. He doesn't care as much about it being FOSS (he's using Unreal for his current game) but it's supposed to just be good. Unreal is an absolute pain to work with.

That said, it's still in early stages. It's usable from what I understand, but even their quick start introduction warns about it and advises people to use Godot if they're looking for a mature, stable engine.