The Nintendo E-Reader was an add-on device for Nintendo's Gameboy Advance system. Each card would have a special code which would enable you to play either a game or download special content.
The main draw were the NES games, except you needed to scan five cards to play even simple games like Donkey Kong.
Excitebike did show up though, so that's good.
Oh and Nintendo somehow thought people wanted to pay for Urban Champion again...
There weren't many NES games to choose from, but Nintendo also tried selling cards to help out your Animal Crossing game on Gamecube.
And Pokemon on GBA.
Some games even had the option hidden. In Japan, they had a contest where fans were given cards to use in Mario vs. Donkey Kong. The cards never made it to America.