LSDJ (LIttleSoundDJ) is a program for making music on the Nintendo Gameboy, compatible with multiple versions of the pocket console - including the original DMG model. It's the most comprehensive sequencer available and it now has a new getting started guide to help new learners! Chip Music maker Infu has provided open-source illustrated instructions detailing how to start making music in the tracker software.
There are numerous ways to sync your Gameboy to external gear, and it can even be controlled via MIDI. Nullsleep is one of the most prominent chip music artists, and was interviewed recently for the 'midierror meets...' podcast.
LSDJ can be run on a computer emulator, meaning you don't need the Gameboy to actually use it - though it is the preferred method. The instructions can be downloaded as a ZIP for offline use and are available to view here: https://learnlsdj.github.io/
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We got a look at it in action
Dreadbox Hypnosis too
6 voices, plenty to fiddle with