Forum user wolke recently posted about his monophonic guitar synthesizer.  This DIY project has an impressive list of features.  This is a German language video that demos the cool effects.  The unique sounds remind me of spaceage music.

The code for the project is posted on Github https://github.com/wolkstein/GitSynth127

The modified audio library is on Github as well https://github.com/wolkstein/Audio

Discussion about the project can be found over on the forum.