HEALPix

HEALPix (Hierarchical Equal Area isoLatitude Pixelation of a 2-sphere), can refer to either an algorithm for pixelation of the 2-sphere, or the associated software package available under the GNU GPLv2 license. Among other features, the HEALPix software implements extremely efficient Spherical Harmonics Transforms and allows quick and accurate simulations and analysis of diffuse signal on the sky (such as the Cosmic Microwave Background anisotropies). Visualization tools are also available.
Find HEALPix at: http://healpix.sourceforge.net