Related link: http://www.levenez.com/unix/history.html
A friend passed me this link.
Éric Lévénez put together a time line of the history of Unix, showing its various branchings, mergings, and other developments, starting in 1969 and ending this month (so it is almost current). You can download the chart in various formats. I printed the 17 pages and taped them together.