Developer: Gammation

Gammation was a small company in Ohio run by programmer Robert L. Esken Jr. It mainly sold rapid-fire adapters for Atari joysticks by mail order, and it released just one game: Gamma-Attack (1983), a shooter in which a hovering saucer attacks tanks on the ground below. Very few copies sold and the company soon closed. Today the cartridge is known as one of the rarest Atari 2600 games, with only one original copy known to exist.
Because its code was preserved, you can play it below in your browser.