The FGT blog offers in three entries his big list of free geostatistical / geospatial software. If I'm not mistaken, this list includes open source software but also non-open source free software. The introduction goes this way: "Now, a series of posts listing a large number of free programs / services for doing geostatistical / geospatial analysis. Programs included will be those that specialize in this area; other general purpose GIS apps with statistical functionality (e.g. SAGA, MicroDEM, gvSIG) won’t be included. Descriptions come from the software’s website or documentation; this has the advantage of concealing my vast ignorance in this subject area. I’ll probably put biologically-oriented software in a separate series. Click on the program title to go to its website."