This is an Arduino project that looks fun to follow. Watch the video to the end for a seasonal touch.
OK, so this isn't really a xylophone but a glockenspiel because it has metal and not wooden bars but it is a fun piece of construction. Unusually, rather than buying solenoids, it goes into the details of how to build them and how they work. The video of creating coil formers and winding the coils is enough to make you want to run out and buy a lathe.
Its a nice Arduino project even if the final result isn't quite as resonant as it should be. The final demos are impressive and its educational as well looking like fun.