It's some sort of first-person voxel renderer, like the classic versions of Minecraft, but with godrays and ambient occlusion. It doesn't look like you can modify the world at all, it's just some basic terrain with some sort of hexagonal structure built over it (?).
It also renders on 30fps, you can go around the world, smoothly.
I wouldn't say 30fps is "smooth" per se, but it's very consistent with no stuttering or lag, so at least the frame times are smooth. :)
(To clarify: it's locked to 30fps, it doesn't only perform at 30fps.)