The prisoner's dilemma tournament is over. There were a total of 21 entries. The winner is Margaret Sy, with a total of 39 points. 2nd and 3rd place go to rpglover64 and THE BLACK KNIGHT, with scores of 38 and 36 points respectively. There were some fairly intricate strategies in the tournament, but all three of these top scorers submitted programs that completely ignored the source code of the other player and acted randomly, with the winner having a bias towards defecting.
You can download a chart describing the outcomes here, and the source codes for the entries can be downloaded here.
I represented each submission with a single letter while running the tournament. Here is a directory of the entries, along with their scores: (some people gave me a term to refer to the player by, while others gave me a term to refer to the program. I went with whatever they gave me, and if they gave me both, I put the player first and then the program)
A: rpglover64 (38)
B: Watson Ladd (27)
c: THE BLACK KNIGHT (36)
D: skepsci (24)
E: Devin Bayer (30)
F: Billy, Mimic-- (27)
G: itaibn (34)
H: CooperateBot (24)
I: Sean Nolan (28)
J: oaz (26)
K: selbram (34)
L: Alexei (25)
M: LEmma (25)
N: BloodyShrimp (34)
O: caa (32)
P: nshepperd (25)
Q: Margaret Sy (39)
R: So8res, NateBot (33)
S: Quinn (33)
T: HonoreDB (23)
U: SlappedTogetherAtTheLastMinuteBot (20)
I agree, my fellow top-ranking-non-source-ignoring player. Saying "nobody could do any better than randomness in this tournament" is strictly true but a bit misleading; the tiny, defect-happy pool with almost 20% random players (the top 3 and also G; he just obfuscated his somewhat) didn't provide a very favorable structure for more intelligent bots to intelligently navigate, but there was still certainly some navigation.
I'm pretty pleased with how my bot performed; it never got deterministically CD'd and most of its nonrandom mutual defections were against bots who had some unusual trigger condition for defecting based on source composition, not performance, or had very confused performance triggers (e.g. O--why would you want to play your opponent's anti-defectbot move when you determine they cooperate with cooperatebot?). Some of its mutual defections were certainly due to my detect-size-changes exploit, but so were its many DCs.