SpectraVideo Compumate — A peripheral for the Atari VCS/2600 which adds additional memory and a membrane keyboard, turning the game machine into a rough equivalent of a personal computer. It has BASIC programming, a draw program, and a music (MIDI) program built into memory, but can also read/write programs on cassette tape through audio inputs (unfortunately, I do not have the audio cables yet).
Here it is attached to my VCS "light-sixer" model: