The project "A Visual Expedition Inside the Linux File Systems" [jhu.edu] consists of a collection of 78 visualizations (e.g. dotplots, bar graphs, treemaps, scatter plots...) and 10 animations that illustrate the relationships among the Linux File Systems through the lens of the external symbols their kernel modules use. The analysis behind the graph was accomplished on 1,377 kernel modules from 2.6.0 to 2.6.29.
The most thorough analysis was done on Daniel Phillips's tree, which contains the latest two disk-based file systems for Linux: tux3 and btrfs. The main techniques used to establish relationships among file systems were hierarchical clustering and phylogenetic trees. The website also contains a set of rankings based on various properties related to the evolution of the external symbols from one release to another, and complete timelines of the kernel releases for Linux, FreeBSD, NetBSD, and OpenBSD.
More at Slashdot. See also Graphing Dependencies in the Haskell Package Universe and Linux Kernel Graphing.