Some call it Outside. It's been in development for the last 14 billion years or so, which is just about the right amount of time to get such a good physics engine it has working mostly without bugs.
Not to mention the superb rendering VR PBR pipeline, which is optimized enough to draw even the most complex scenes at a few thousand fps on literally any hardware.
It's essentially a fully voxel-based engine that doesn't even use meshes but renders the voxels directly to pixels - which is enabled by having very small individual voxels. The chunking is unusually large however, which may lead to some bottlenecks when doing large open worlds.
While there are a few mesh-to-voxel plugins in beta development by the community, they still aren't quite there yet. I'll rather wait for a full release.
The core development team isn't really working on the engine anymore though, so it's pretty much closed source abandonware.
P. S. If you're gonna do anything with quickly rotating stuff, note that there's an animation bug that still hasn't been fixed.