The Rainbow HAT was developed for Google developers to play around with Android Things. It is a HAT for the Raspberry Pi that uses as many different protocols as possible, including SPI (the APA102 LEDs), I2C (the BMP280 sensor and 14-segment displays), GPIO (the capacitive touch buttons and LEDs), and PWM (the piezo buzzer).
Rather more simply, there are a lot of inputs and outputs that you can control, using different ways of sending data between the Raspberry Pi and the Rainbow HAT.
We developed a set of activity cards at the time we launched the board, but now we've revised and reprinted them, and the contents are also available as a series of tutorials linked from here. The cards are available on our shop, including a teacher booklet, if you want an offline copy or a reference set. They are also bundled with the Rainbow HATs in the education pack, again including a teacher booklet with solutions and development ideas.