General MIDI Player is an easy way to turn your Mac into an instrument, using its built-in General MIDI support. Starting in version 2, it also plays back type 1 General MIDI files!
You can play the General MIDI instruments using either your mouse, computer keyboard (including support for non-US keyboards), or MIDI device (both hardware and software MIDI devices supported). You can even play along yourself while a General MIDI song plays at the same time. It has a simple, one-screen interface, that will let you start making music with your favorite General MIDI instrument in seconds!