30. USCF Chess (Intellivision)
Significantly faster and stronger than Atari's offering, this program plays a pretty decent game of chess. I'd beaten most of the difficulty levels on real hardware a while back, but when I took on the highest difficulty, Level 6 -- which takes hours and hours, though not as long as the Atari -- I ran into a game-breaking bug. And in fact, the bug was reproducible in emulation, so that put me off for a while.
But today I tried again, and finally beat Level 6 with the White pieces, and then again with Black. For whatever reason, my opening choices didn't put the game onto a bug-triggering track. I was using emulation with a 20x speedup, so the games went along fairly briskly -- 80 minutes realtime for the first one, 140 for the second game. My win with White was fairly routine, but the Intellivision had me on the ropes in the second game, and probably had a near-winning position before it lost the thread. Still, it took 81 moves to earn the victory.
This is another case where giving a grade seems silly, but then again it's a pretty admirable effort, so 8/10. (One point off for the game-breaking bug, and one point off for being fairly deterministic.)