So I've been working on a synth on and off for the last 2 years. It's finally starting to take shape and once I finish sourcing parts and figuring out the audio opamp/output circuit and interface I'll be releasing it.
Thought I'd share my progress so far:
It's a 4bit synth that doesn't use a static sample rate frequency to generate the synthesis sound- therefor it doesn't have the usual artifacts from low sample-rate dsp so that no aliasing is generated, and no anti-aliasing algorithm is needed.
Originally built on the Arduino- I moved it to the ARM-based Leaflabs Maple to take advantage of the faster clock for higher pitches.
It currently has 3 synthesis types:
1. 32 step wave synth with digital filter (kind of like the LSDJ wav synth)
2. 128 step PWM synth
3. 256 step LFSR noise generator (like a gameboy or NES noise- only the pitched noise is in tune)
All modes have a sub oscillator & oscillator sync to give it some extra tonal quality. I really liked the idea of a LFSR noise generator with oscillator sync. 
I'm just about done with main synthesis code and am about to start on an interface. Been thinking about using a 4dsystems tiny tiny OLED display module and a single pushbutton/encoder knob, as well as 4bit sample playback and storage using a micro sd reader.
Here is the demo of it I recorded this weekend, be sure to download the original waveform- soundcloud/mp3 conversion added artifacts. http://soundcloud.com/trash80/codename-sqrt-synth-test
\o/
