A cheatsheet for the most popular microcontroller chips' pinouts, connection headers, and cable pinouts.
The SwinSID is a pin-compatible and software-compatible replacement for the Commodore SID chip based upon an Atmega microcontroller. You can drop this chip right into a socket on the motherboard of a damaged Commodore computer, or you can probably drop it into a hardware synth that uses SID chips and hit the ground running. The firmware image and schematics are available for download for free on the website, so you can roll as many of your own as you want.
Plans for constructing an Arduino shield which lets you stack another Atmega 126 or 328 in master/slave configuration. Double the I/O pins, double the interrupts.