The Magnavox Odyssey Multicard is a multi-game circuit board, designed by Ben Spenger (Boojakascha), which allows all twelve original Odyssey game cards — and therefore all Odyssey games and homebrew — to be played from a single card.
The original console works on short circuit and interruption, which alters the game logic of the main unit. By plugging in the multicard, the user "short circuits pins 4 and 2 which powers the system on". Then the user reads the white instructions on the face of the PCB, and recreates different games by flipping DIL switches (also on the face of the board).
Boojakascha has provided files for its reproduction, and corresponding instructions at http://boojakascha.ch and AtariAge.com
Setup
Simply insert the multi-card into the console, as though it were an original Magnavox Odyssey game card, with the DIL switches facing away from the console. To switch between games, remove the card from the console, and adjust the DIL switches accordingly.
There is no difference in the operation of the controls, as compared to original Odyssey game cards.