In 1982, the short-lived American company Starpath released a cassette tape-based peripheral for the Atari 2600 called the Starpath Supercharger. The games were written onto cassette tapes and inserted into a cassette tape player cartridge that when plugged into the console gave it roughly 6 kilobytes of RAM (as opposed to the standard 128 bytes), and had a wire to connect to the cassette player through its headphone jack. This allowed the Atari to play more complex games and process more sounds and music than its standard cartridges. Only 10 games, all of which having been developed and published by Starpath themselves including a port of Konami's Frogger, were officially released for the peripheral, as they merged with fellow developer Epyx in 1984.
The Atari 2600 was the first video game console to have wireless controllers. The Atari CX-42 joystick controllers used radio waves to transmit information, and they released in 1983.
It is possible to play an Atari 2600 using a Sega Genesis controller. The reason why the Sega Genesis controllers work on the Atari 2600 is because both the Genesis and the 2600 use DE9 ports. These ports were a popular type of port, and were used for the Sega Megadrive, the Atari 7200, Commodore 64, MSX, and the 3DO.
There was going to be a peripheral for the Atari 2600 called the "Mindlink" that made it possible to play games with your mind. Atari said the device would allow users to "think" the movement of objects on the screen. The product however simply read electronic impulses in the forehead whenever the user moved their eyebrows, rather than actual brain waves.