Watch how the community based GRASS GIS software development works! You can see how the individual contributors modify and expand the source code.
The corresponding timeline is available at http://grass.osgeo.org/devel/grasshist.html
Download the high resolution version from http://grass.fsv.cvut.cz/video/
I wish I could post a more useful comment, but… THAT IS REALLY COOL!
Very nicely done.