The PiGlow is a small add on board for the Raspberry Pi that provides 18 individually controllable LEDs. You can use it for all sorts of things! And of course, it fits inside a Pibow!
There are tons of things you can do with it:
If you just want some Python code to start tinkering with please check out our GitHub repository which also includes the full datasheet for the IC used on PiGlow.
Gordon Henderson has added a PiGlow driver for wiringPi which you can find here: http://wiringpi.com/dev-lib/piglow/
Simon Walters has added PiGlow support for Scratch which is here: http://cymplecy.wordpress.com/
Jason Barnett has put together a great Python class and a load of samples: https://github.com/Boeeerb/PiGlow
Ben Lebherz has forked Jasons project and tidied up the code a bit while adding gamma correction: https://github.com/benleb/PyGlow
Manuel Ernst has created a Node.js library: https://github.com/zaphod1984/node-piglow
Falldeaf has put together a nice XBMC hack to use the PiGlow as a status indicator: http://falldeaf.com/2013/11/the-xbmc-piglow-information-display-addon/
This board uses the SN3218 8-bit 18-channel PWM chip to drive 18 surface mount LEDs. Communication is done via I2C over the GPIO header with a bus address of 0x54 (Python example code provided). Each LED can be set to a PWM value of between 0 and 255.