Is there a way to sync music between a PowerPC Mac and an iOS 7 device? My friend has a G5 running 10.5 Leopard (the last supported version of OS X on PowerPC). However, after updating to iOS 7, syncing is no longer supported, as iOS 7 requires iTunes 11, which in turn requires 10.6 Snow Leopard.

Is there any way to get music sync functionality back on a PowerPC Mac without reverting to iOS 6, whether through some version of iTunes, or a 3rd-party tool, and without jailbreaking?
There are many apps that can move data on and off an iDevice, albeit not in the same "sync" model that iTunes uses. Try the trial of iExplorer, for example.