Before the Guitari, I did make a working prototype board of another synth - the GAIN BOY. What was the "Gain Boy"? Well, it was a guitar synthesizer pedal based around the CD40106, scalable via a rotary knob, and it's one I plan to revisit. I called it that because the layout on the breadboard looked like it'd fit into a pedal roughly the size of a Nintendo Game Boy "Grey Brick" variant, which would have made for an AWESOME case design.
I got really obsessed with learning CMOS guitar synth wizardry from Parasitstudios on Instagram/his site. He has an awesome tutorial on making pedals there. I seriously wanted to build my own guitar synth like his 4096 guitar synth, but I could never get the circuit to work as intended on my boards at home.

The Circuit sounded a lot like a Game Boy, hence the name. It had that sort of "Juice Box" audio quality to it that I really liked.