I recently needed to play music in Ruby in order to create an alarm clock of sorts. The code to do this was (surprise surprise) fairly simple, but I want to post it for posterity.

require 'win32ole'  
player = WIN32OLE.new('WMPlayer.OCX')  
player.OpenPlayer('C:\alarm.mp3')  

This will open a new instance of Windows Media Player that plays the selected song.

Note that win32ole should be installed by default, and does not need to be installed as a gem.