I would recommend the David Ellefson Rock Shop app, it's a fine app, has a couple of different bass & guitar amps on it (if you know who David Ellefson is, you'll know he uses Hartke stuff mainly so the main bass amp on there is made to look like one of their Hydrive stacks). Has a built in tuner, couple of effects and you can play any songs you have on your device through it to play along to.