MacLight 
MacLight lets you control the keyboard-LEDs (capslock, numlock) on your Mac.
Screenshot

Installation
$ gem install maclight
Usage
$ maclight --help
Usage: maclight <command>
MacLight v1.0.0 - LED control utility
Options:
--version: Print version and exit
--help, -h: Show this
Commands:
keyboard Control keyboard LEDs
API Usage
#!/usr/bin/env ruby
require 'maclight'
# Turn both LEDs on
MacLight.capslock(true)
MacLight.numlock(true)
sleep 2
# Turn both LEDs off
MacLight.capslock(false)
MacLight.numlock(false)
Credits
MacLight is based on HID demonstration code by Amit Singh.