I'd like to get a low power pc (arm or atom) running linux and control the music that it plays through an android app, effectively becoming androids version of Logitech's Squeezebox. I'd prefer not to install X Windows on the box. Has anyone heard of such an app?
I'd recommend installing mpd on the linux server and an mpd client on the android device.
The squeezebox server software doesn't play audio directly so you would have to either install a player like SoftSqueeze or SqueezePlay on the server, or use another music application to play the mp3 stream.
You didn't ask about it, but if you want to play music stored on linux server through your android, you can also install the squeezebox server (now called Logitech Media Server) on the same linux server, and install Squeeze Player on your android along with any squeezebox controller app (I've found SqueezeDroid and SqueezeControl to be best).
Android's version of Squeezebox... is Squeezebox! I do currently use my Android phone as a remote for my Squeezebox.
I've got the Squeezebox server installed on my server, and I have the Android SqueezeControl app installed on my phone. It's handy for skipping unwanted tracks from another room, and for starting the music playing before you walk through your front door.
You can also connect to the MP3 stream that Squeezebox broadcasts to listen from your phone.