Thanks to Brandon for letting us know about this Atari Synthcart Player! From Lab away from Lab:

The Atari Synthcart Player is designed to offer flexible control over the Atari 2600 as a musical instrument. The Synthcart Player is a hardware controller tailored to work along side the phenomenal 2600 software Synthcart written by Paul Slocum. As such, this hardware is not a sound generator but rather expands the Synthcart user interface, provide note sequencing with various timing options, and connects directly to the left controller port of the Atari 2600.

The Synthcart software was written to accept inputs from the 2600 keypad controller, which offers twelve pushbuttons. A midi solution was designed and at one time manufactured by the folk(s) at Highly Liquid. I built and utilized these midi mods but wanted something simple and custom for use with the 2600 and Synthcart.

For this project, I had a few constraints:

• Control the Atari 2600 through emulation of the 2600 keypad controller
• Allow hardware-based user inputs and feedback akin to classic 16-step sequencers
• Provide midi clock input to effectively control Synthcart timing from other midi-based musical instruments
• Package the hardware within the miniaturized Atari 2600 Flashback case

Read more and see more on YouTube