AVR MultiTool

You’ve just got hold of the latest whizzy IC and can hardly wait to start experimenting with its functions. It is highly likely that, like many modern devices, it will be controlled over an I2C or SPI interface.
What would be useful at this point would be some kind of versatile hardware tool based on a microcontroller that could talk to these interfaces, as well as providing a few digital I/Os and perhaps also a PWM output.