Block iTunes (or other apps) from opening when Spotify is open. Gets rid of that pesky "oh you hit the play button? Better open iTunes" behaviour.

iTunes.rb

#!/usr/bin/env ruby

# Blocks iTunes from launching if Spotify is open
#   Installation:
#   sudo ruby -e "$(curl -fsS https://raw.github.com/gist/613045/b12123d5e25d446038e6300bf54d2121bf180c34)"

blockers = ["Spotify"]
launch = true
blocker_name = ""

IO.popen("/bin/ps -x") do |output| 
  while process = output.gets do
    blockers.each do |blocker|
      if process.include?(blocker)
        launch = false
        blocker_name = blocker
      end
    end
  end
end

if launch
  spawn = fork do
    %x['/Applications/iTunes.app/Contents/MacOS/iTunesReal']
    exit
  end
else
  puts "Not launching, #{blocker_name} process found."
end