Here’s a Rad-Fi patchable synth partially assembled on my kitchen table. It’s a kit from Bleep Labs that comes with all the components needed to create a simple digital/analog synth. It took me somewhere between 3-5 hours to put the whole thing together following the instructions from the Bleep website.
And here’s the fully assembled Rad-Fi synth ready for noise making. It supports MIDI input and has two pre-programmed ATMega328 chips that enable record/playback and signal processing functions. Hackaday has some material for making modifications to the basic design as does the analog guide on the Bleep site.
Overall the Rad-Fi falls more into the category of educational tool than musical instrument and seems like a very accessible way to begin learning about electronics and synthesis.