Nasturtium Labs has released Nasturtium Player, a minimalist Mac app that plays YouTube music videos alongside your own iTunes tracks. It’s available at the Mac App Store for US$2.99 for a limited time; the regular price is $4.99.
A short demo video and additional screenshots can be found at: http://nasturtiumlabs.com/player/press.html. To purchase Nasturtium Player go to http://tinyurl.com/bz688s4 .