Twisten is a new music service from the creators of Grooveshark. If you're listening to something and want to share it with your friends on Twitter you can simply type in the track name and it will automatically add a link for playback inside a tweet. Anyone who clicks it can listen to the entire thing for free over at Grooveshark Lite.
The service keeps an eye on Twitter for mentions of music tracks people are listening to and cross references the titles and artist information from the Grooveshark music database. If it finds a match, it inserts an embedded music player so you can listen to the track right there.
There are two sides to the service, one that culls everyone's tweets, and one for just your friends. In my case it only pulled up a single track from the 300 or so people I keep an eye on. Presumably if you have more friends (who post a lot of music) you'll find more things to listen to. The service also lets you bookmark tracks you like and send them to friends. You and your recipients have the option to listen to it in Twisten, or back over at Grooveshark Lite.
While neat, I didn't find the service as useful as Songly, which lets people download the music track you're sharing. It is, however, a far more automated process that won't require your friends to use something outside of their usual Twitter routine.