An absolutely massive interactive HTML-based graphic shows the timeline of your favorite Linux distributions.  With the left side presenting 1992’s Debian, Redhat, and SLS, it shows how the various distributions we know today came into existence.  Follow the lines to the right as they branch into CentOS, Fedora, Tinfoil Hat, Knoppix, Freespire, and many many more.  Click on each name to be taken to the home site for that selected distribution.

A great way to visualize the massive fork and merge trees of Linux.

GNU/Linux distro timeline.