I recently stumbled on a really fantastic free tool called gource. Gource displays code as an animated tree with the root directory of the project at the centre. Directories appear as branches with files as leaves and developers can be seen working on the tree at the times they contributed to the project.

I’ve had a lot of fun looking at the history of various projects. Here’s the history of AquaQ’s TorQ:

Or the entire history of Unix since 1970! (if you have about an hour to spare)