its primary function is that of a internet clock radio
in this case a Reciva based radio might be a good solution. You will find a comprehensive list here
But beware: not all models will correctly deal with a power outage. Some (if not most) of the Reciva based models in such a case do not automatically reconnect to your network and thus will not adjust the time and therefore fail to wake you up on time.
At least the Logitech Squeezebox Radio will play internet radio without any server software running and I'm quite sure this also applies to the Squeezebox Boom.
It might be worth the effort to have a look at Freecom's MusicPal
or Terratec's Noxon devices
However, don't expect any of the alternatives to work as smoothly as your SoundBridge Radio. Roku's products, although quite old and now EOL are still very much state-of-the-art.