From Vox:

amPlug3 is the third generation of the amPlug series, the headphone amplifiers that can simply be plugged into a guitar and used right away. With a variety of amp options and guitar tones available, Amplug offers an ideal solution for guitarists and bass players to practice with the best tone while keeping things simple. Remember, every guitarist has to practice and with the expanded range in the amPlug 3 series, guitarists and bass players can have more than one!