Choplifter

The Atari 2600 version of this famous Brøderbund game was mentioned in several internal Atari documents and appears to have started to go through the process of getting box artwork made. In fact, a mock-up box for Choplifter even appeared in a Canadian ad (see below). It is estimated that this prototype is approximately 50% complete. It is unknown if any further work was done on Choplifter or if it was even finished before being cancelled.

Technically speaking, this game is not really NTSC, because it counts 295 scanlines.