It uses the amazing AMY Synth engine for everything sound-related - check it out!
The keybed is a low-profile mechanical keyboard (in my build I used Keychron Low Profile Silent). It also has a joystick for pitch-bends and 16 pots.
The hardware files are in a separate repo. Big disclaimer: at this stage this is not an easy DIY build, it's a prototype with a rat's nest of wires inside. I am planning a v2 with custom PCBs for everything, right now i'm using a custom PCB only for the pots.