GrooveMac is a nice GrooveDown.me package for OSX.
GrooveMac package guidelines:
Step 0: Download and install XCode.
Step 1: Open up 'Icon Composer' and open icon.icns, fiddle with to your liking.
Step 2: Open up 'Jar Bundler', select your GrooveDown jar and set the icon to icon.icons.
Step 3: Hit 'Create Application..' you're done.