You can currently find lots of application and websites on the Internet where you can create playlists that match your taste, and share them with your friends. The thing that was lacking was an application that lets you comment on the songs as you listen to the tracks. Milkshake is a curious program with which you can create lists of three songs and comment on them with your friends in real time, thanks to the integrated chat. This way, you can know what your friends think about the three songs, in a simple way and without delays.
The songs can only be added from YouTube or SoundCloud, but that's more than enough to have a wide range of options. Milkshake lets you listen to the songs before you add them to the list, and talk to one friend who you can't write to until he or she gets in the chatroom.
Despite its limitations, Milkshake is a tool that does what it says it does: it lets you comment on songs with your friends in real time.