I really like the sounds that Gijs is able to produce with his Hardware Software Synthesizer 2, aka the HSS2. It’s all based on a single Arduino, making this version easier to build compared to the HSS1. Check out the link for the complete code and schematics so you can make you own.
This is a trimmed down version of the hard soft synth 1. The hss1 used 2 arduinos, one for sequencing and one for audio. This version has both the sequencer and the audio in one arduino, reducing the number of parts allot.
More about the Hardware Software Synthesizer 2
In the Maker Shed: Make: Arduino