Providence-based maker and co-author of Getting Started with Raspberry Pi Shawn Wallace has a great-looking HAT design for Raspberry Pi currently crowdfunding on Kickstarter. The board adds a ‘mess of inputs’ to the Pi, and includes two MCP3008 ICs for easily interfacing with Pure Data and other programs. (The campaign also includes a peripheral reward for LEGO Mindstorms – this is not related to the Pi.)
It isn’t an IO Board, it’s an “Oh Eye” board: sixteen 10-bit analog inputs and 8 digital inputs/outputs pulled out. It makes it easier to use the Pi as part of a special purpose appliance or musical instrument. The analog inputs are via two MCP3008 chips connected to the Raspberry Pi’s hardware SPI interface. The use of this ADC chip with the Pi is common and well documented. You may ask: “isn’t 16 channels of analog input a little overkill?” To which I would answer: yes it is, except when it isn’t.
There’s also a version available for the Pi Zero: