The idea behind Game Brain (Model C-700) was clever: Atari would use surplus CPUs from their unsold dedicated consoles, such as Pong, and build a new system which would play ten particular game titles. As an interesting design choice Game Brain's controllers were fixed on the console itself and would not detach.
The planned games were mostly variations on the megahit Pong. The complete list of titles reads as follows: Pong, Stunt Cycle, Super Pong, Super Pong ProAm, Super Pong ProAm 10, Super Pong 10, Ultra Pong, Ultra Pong Doubles, Video Music, and Video Pinball.
The nature of the recycled hardware meant Atari could not shift huge numbers of the console, but this was never their strategy anyway. In any case, the bigger problem was that when Atari finished the Game Brain, the industry had already moved on from consoles with built-in and predefined games. So, instead of launching the system, the company cancelled the project in 1978 and concentrated on Atari 2600 (Atari VCS) and its followers.