Pong written in 6502 assembly, able to run on an Nintendo Entertainment System
The nesasm compiler was used to compile pong.asm into a ROM (pong.nes).
I recommend using the FCEUXD SP NES emulator. It includes a bunch of features to see whats going on in the registers and graphics nametables and all that jazz.
-NOTE- FCEUXD is Windows only. NEStopia is a viable alternative for Mac. I used Wine + FCEUXD to develop, but it did result in some stuttering when playing the game.