I have used the Gource tool for a few years now to produce visualisations of project history. The results are pretty but not especially informative and mainly serve to show how well maintained a projects revision control history is.
Recently I noticed the Gource tool got updated and I decided to compile it and give it a try. After the usual building of the dependencies (including all of libboost!) the new version (0.38) gives much better results than the previous edition I had been using (0.27).
I tested it on the NetSurf git repository generating an overview for the whole ten years the project has been running which produced a six minute video which I shall be using on the NetSurf stand at our next show.
Overall if you need a historical visualisation of your projects revision history Gource is a pretty good tool. I have also used the alternative "code swarm" tool in the past but that seems to have bitrotted to death so I cannot recommend it.