The dimmer can be used to control the intensity of lights. It works the same as regular dimmers that can be bought in any other hardware shop, but can be controlled over I2C. It should work with any I2C-capable device, including the Raspberry Pi, Arduino and many other microcontrollers.
The dimmer can be found here in the shop.
The dimmer is at I2C address 0x9E. Port 0x10 is the intensity. The value written can be between 0 and 255, where 0 is the lowest intensity and 255 is the highest intensity. With bw_tool it can be controlled like this:
bw_tool -I -D /dev/i2c-1 -a 9e -W 10:xx:b
Where xx is the intensity in hex. (i.e. 00-ff, 80 is "half", 40 is "quarter" intensity).