Atraci is licensed under the MIT license, so it's free software.It's not in the normal ubuntu repos afaik, so that might be the reason why it's not in trisquel. That said, it basically plays the sound of youtube videos... which is really nice, but it's not a real streaming service like spotify.
There is www.jamendo.com which offers a few really nice songs...however, normal streaming services impose DRM and i guess that's not really compatible with free software...
