What feels like many lifetimes ago, when the emulation scene for the Atari 2600 was pretty grim, I decided to spend some time putting together an emulator to allow us to run Atari 2600 games on a PC. Although I managed to get many games to work, I was eventually beaten to the finish line of "usable by the general public" by a couple of other projects, and decided to move on to other endeavors.
Looking back on this code with a whole career of design and coding between now and then, there are certainly some embarassing things in here. But some of the approach (especially with the table-driven 6507 emulation) has a kind of elegance in its simplicity.
The code targeted DOS and X-Windows, but I'd be surprised if any modern compiler would put up with its pecadillos. As such, there are no build instructions. If you want to get this to run, you'll be doing some new work. :)