I've just put my first beta of an Android tablet-based synthesizer on Google Play:
"SynthPad" - allows for quasi-theremin effect, and switches to modulate other audio parameters
Touch-drawn sound waves and envelopes
3 filter stages
A bunch of other stuff.
If nothing else, it is genuinely a lot of fun. And it's free.
I am open to suggestions in terms of UI, features, Pd usage. Really anything. Let me know what you think. If you like it, I wouldn't mind a review. (I'll be making a non-tablet version eventually).