Kid Vid Voice Module
The Kid Vid Voice Module was an add-on created by Coleco and was released for the Atari 2600 in 1983. It was similar to the Intellivision Voice Synthesizer, where it had games that could actually talk and have voice acting, which was a new and revolutionary thing for the time. The games were on cassette tapes rather than cartridges and you put it in the module and the game would tell the tape what to play based on the actions you did.
Why it Flopped
A grand total of TWO GAMES were made for the system. It also didn't really add anything to the game other than voices if you look at it today.
However, it was quite revolutionary for the time, and it actually did what it was supposed to do. The voices themselves also sounded much better than the Intellevision Voice Synthesizer.