Curt Vendel (who’s been groveling through a bunch of old Atari backup tapes for a number of years) has found and posted the source code to the Atari 800 version of Donkey Kong.
Here’s a pointer to the forum thread: link
Update: Mirrored here.
Certainly brings back memories. There’s less code than I remember, and some bits of it are really a mess, but it’s fun to see this again. I should add that you’ll just see a bunch of assembly code, with not a whole lot of insight into how the game was actually developed (when I finally got to see the source for Quake, I remember feeling somewhat disappointed — “That’s it? My God, that’s a stupid hack.” If you take the trouble to look, I’d not expect revelation, just a bunch of code written by a young guy in a hurry).