Serenade is a new iPhone and iPod touch app from a company called Crist Drive—a reference to the Jobs family garage where Apple was founded 33 years ago—hat allows you to share tracks you're listening to with others. With a tap, according to the developer, you can send a song via Twitter and email or copy the song information so you can paste it anywhere else. Along with your message, Serenade adds a link to your song so your friends can listen to a preview and, if they choose, buy it from iTunes. The app is free and available here.