ILWIS is a sophisticated GIS package that was released as free and open source software on Monday. While the open source version is available from 52North, there’s an add-on software package for ILWIS currently only available from the original ITC website. AHAS (AVHRR Hydrological Analysis System) works with ILWIS for analysis of data from the Advanced Very High Resolution Radiometer currently flying aboard many US and European satellites. Analysis products are biophysical (e.g. NDVI, Fractional Vegetation Cover, Crop Reflectance, etc.), climatic (Daily Radiation, Sunshine Fraction, Soil Heat Flux, etc.), and hydrological (Potential Evapotranspiration, Volumetric Soil Water Content, etc.). AHAS requires ILWIS to function properly, and will ask for the location of the ILWIS executable the first time it starts up (it first looks in C:\Program Files\ILWIS3.1\ for the Ilwis3.0.exe executable file).
Unfortunately, while AHAS is free, free multi-band AVHRR data is hard to find, especially recent data; if anyone knows of good free sources for this data, please post them in the comments section. You can buy AVHRR data directly from the USGS.