Ported from https://code.google.com/p/simplexnoise/ because it's not going to be around much longer.
From the page:
Perlin simplex noise generator for generating improved Perlin noise written in C# with no external dependencies and released to public domain. Includes generators for 1D, 2D and 3D.
Simplex noise generator has several advantages over standard Perlin noise, most notably:
- Computationally faster.
- No noticeable directional artifacts.
License: public domain.