Alan Turing's hand-drawn Monopoly board, the Turing Papers, Bletchley Park, UK.jpg
Update: William Newman has the true history of this artifact: "May I confess to being the perpetrator of said 'board', which I drew on a sheet of paper back in the 1950s when I was in my early teens and lacked the money to buy a proper set. My brother and I played on it, and when Alan asked if he could join us in a game we played a threesome (Alan lost). Later the board fell into disuse and I lost track of it about 50 years ago, but it recently turned up (together with the rules), see www.bletchleypark.org.uk/news/docview.rhtm/644565. The Roman numerals indicated property prices. I forget why I added the diagonal. "