http://uniblock.tumblr.com/post/97868843242/noise
"Our game needs 3D noise for terrain generation, particularly cave generation and cliff/arch/overhang generation. [Simplex noise is patented, so] that leaves us with two options: Take the easier and less-interesting route and deal with the artifacts of Perlin noise, or create something new. So I took the latter route, and developed a new noise algorithm for us to use called OpenSimplex noise."
https://gist.github.com/KdotJPG/b1270127455a94ac5d19
(Late edit: updated image to reflect how the updated algorithm looks)