Gstat is an open source computer code for multivariable geostatistical modelling, Prediction and simulation, and has been around from 1997. In the original form, gstat is a stand-alone executable, interfaced to various GIS. As of 2003, the gstat functionaly is also available as an S extension, either as R package or S-Plus library. Current development mainly focuses on the S extension. The reason for this is obvious for those familiar with R and/or S-Plus.
