I was first exposed to GRASS GIS in college. It was developed by the US ARMY Corps of Engineers, and has since become a popular free software development.
When it comes to using raster maps in a GIS, GRASS is effective and easy to use. While at the Direct Readout Laboratory (NASA GSFC) I deployed a 500M GRASS GIS for the entire planet using readily available base maps and free data sources. At the Direct Readout Laboratory we used GRASS with GEOTIFF data products created at DRL from data acquired from the Aqua, Terra and NPP spacecraft. One interesting development was the use of a GRASS GIS to create an animated demo of our data products that amounted to overlaying acquired data products in a near real-time. The excellent command line and scripting environment offered by GRASS allows fast and easy use of built in functionality in combination with shell scripts and programs written in C, Perl, Python ,Java , etc, making it an extremely versatile environment for GIS and remote sensing.
One fun, and interesting project which I worked with at home was the creation of AVI "movies" of overlaid GEOTIFF scenes for specific data products. The process involved; acquiring daily GEOTIFF products from NASA/DRL via the internet, then using a home built Beowulf cluster, importing the GEOTIFF data into a GRASS GIS. Once sufficient data was acquired, GRASS was used to make JPG frames that were later processed into an AVI movie on a workstation using mplayer. A couple of proof-of-concept videos were made after acquiring a couple of months of data. Eventually an entire year of data was acquired, but the emphasis of my efforts was shifted to other things and the idea was shelved due to a lack of time.
Click HERE to download an AVI of sea surface temperature data created using GRASS GIS and a 12 node Intel ATOM Beowulf cluster named "Proteus".