Helium is a UPnP control point that is supposed to accompany Rygel, but can of course work without it. It offers browsing of media servers, selecting a renderer from a list of devices available on the network and can (currently) play back a single media files from the current server listing to the currently selected renderer (by long-push). This is supposed to change in short-term, giving proper playlist and player controls. Also it needs to get aware of servers and renderers disappearing from the network and get some proper error reporting.
Where’s the code?
Current state is available at Gitorious