Check out a few of the example applications that come with HyperMIDI:
Juke Box is a standalone application, written in SuperCard, that plays MIDI files. Just place MIDI files into the Juke Box Folder, and they appear in the Juke Box. Click a song title to play it or stop playback.
Strummer is a HyperCard stack that lets you build guitar-voiced chords on screen by dragging and positioning "fingers" on a fretboard. You can name the chord and save it as a chord representation—click on any chord to hear it "strummed" on your MIDI synthesizer!
Fractal is a HyperCard stack that creates computed music, using a fractal algorithm to choose notes from any scale you give it. Give it the number of voices to generate, possible note durations and timing per voice, and it generates the notes while you listen. Save the generated sequences to MIDI files and import into your favorite sequencer for further editing.
Delay FX is a real-time MIDI effects unit written in HyperCard. You get four independent delay units, with transposition and velocity scaling. You can even send the echoes to different synthesizers or voices for a powerful polytimbral effect!
SPX-90 ed/lib is HyperCard patch editor and librarian for the Yamaha SPX-90 and SPX-90II effects processors. Access and edit any SPX algorithm—reverb, echo, pitch shifting, chorus, and all—and hear the changes immediately.