After months of reports and speculation, Twitter finally launched its music discovery app, Twitter Music, on Thursday.
The app allows Twitter users to discover music that their friends are listening to, to see what artists they follow are listening to, and to tweet songs from the app. It will be available Thursday for download from Apple's App store, or as a web service in the U.S., the U.K., Ireland, Australia and New Zealand, and then it will roll out to Android devices and other countries.
This app is built on the fact that music is a huge topic of discussion on Twitter and music artists are the most-followed Twitter users.
"It uses Twitter activity, including Tweets and engagement (retweets, comments), to detect and surface the most popular tracks and emerging artists," Twitter said in a blog Thursday written by Stephen Philips, the founder of We Are Hunted, the music discovery service Twitter recently purchased.
Here's how it works: The #NowPlaying window allows users to see what songs have been tweeted by artists and other people you follow. Users can also click on a band's avatar to see their top song, to see what other artists' music they've been listening to, or to listen to their music.
Right now, the music on the app will come from Apple's iTunes, or from subscription services Spotify or Rdio. Users can hear previews on the iTunes store and then click to purchase the song.
If they're subscribers to Rdio or Spotify, they can log in to listen to full tracks. Twitter said, "we will continue to explore and add other music service providers."
There's no revenue stream yet. The app will not include ads—for now. The app will presumably drive significant purchases to the iTunes store, and could also lead people to start paying for subscriptions to Spotify and Rdio. Twitter could take a percentage fee for promoting these purchases, but there's no indication that it's arranged any revenue split yet.
So why is Twitter launching this app if it's not currently making money? Anything that makes Twitter users more engaged with the service and gets them to spend more time in the Twitter ecosystem is a good thing. Twitter wants to be the destination for music discovery, as well as the destination for straight-from-the-horse's-mouth updates from public figures, news outlets, celebrities, and friends.
What's next? We can expect Twitter to offer additional ways to purchase music, say from Amazon, Google, or XBox music. And down the line we may also see ads recommending songs for download or promoting ticket sales for certain concerts.
All that information about what music people like is valuable, and based on the success of targeted "promoted Tweets" and "promoted Trends" Twitter will likely look for ways to use that information so marketers can target consumers with relevant messages, without interrupting the experience.
A Twitter spokesperson told me the company is excited to launch this "stand-alone app around a separate vertical."
Though music is the obvious first area for Twitter to tackle, there are various other natural spaces for it to expand—like TV. Twitter is the go-to destination for people to talk about live TV in real-time, so there could be ways to break it out as a vertical, integrating clips and coordinating with live events.
—By CNBC's Julia Boorstin; Follow her on Twitter: