Fountain 3D is a little J2ME toy and a technology demo for a custom-made 3D wireframe engine with some benchmarking abilities thrown in. The camera is fully controllable by the user together with the simple particle simulation. The software doesn't require hardware acceleration; all J2ME compliant mobiles are supported.
Guitar Trainer is an application for mobile devices that helps musicians learn the fretboard of their stringed instrument thoroughly. It supports guitar, bass, banjo, ukulele, mandolin, and cavaquinho (in standard and alternate tunings). It includes a training mode, a game mode, and a tuner. It should work on any Java device supporting CLDC 1.1/MIDP 2.0.