The Mattel Intellivision Controller

Intellivision - Intelligent Television. While other systems were designed around playing games, I think the Intellivision may have originally been envisioned as the evolution of television - as in, interactive television. At least, that may have been the original concept idea behind the system.

With such a departure, they also designed the controller in a very untraditional way. It's more like a television remote control of the time than a traditional game controller.

Aside from two buttons on each side of the controller, it also features a numeric keypad which is meant to allow a more advanced selection of input from the player. Each game also came with overlay cards that can be inserted into the keypad, to display game-specific designations for the 12 keypad buttons.

The other unique departure is the control disc. Unlike other controllers, and even later directional pads, this one is not just 8 directional but capable of resolving 16 directions of movement.