From the Tindie blog:

OKAY Let’s Make a synth!

The OKAY is an analog squarewave synth, ideal for DIY fanatics who want to make big basslines and searing leads! It has a full range of tactile switches and is super portable thanks to being battery powered, so if you need a squarewave synth to go, OKAY is where its at!

The OKAY synth can be played at home or on the move, as it comes with a built in amplifier, speaker and audio output for headphones or recording. You can select through a full spectrum of tones over 6 octaves, mapped across 2 full octaves of keys — for wide-ranging playability off the back of a 9V battery!

Squarewave synths are the go-to sound if you remember the days of Commodore 64, Atari ST and Amiga — making chiptunes on trackers! There is no sound like it, and using the audio output gives you the chance to run it through some pedals and outboard effects.

This educational, hack-able, 3D-printable synth hales from San Fransisco, California and comes in kit form, with PCBs, electronics components and assembly guide. If you own a 3D printer, you have access to all of the STL files on Thingverse to create your own keys, enclosure and other mechanical parts.