MIVI is an unusual plug-in that loads as a VSTi but doesn't actually make any sound or manipulate sound in any way. Instead, the plugin takes the MIDI input and visualises the output in the form of OpenGL 3D instrument (a 3D piano or flute). The goal is to show aspirant musicians (including the musically illiterate) how the score relates to the instrument and how to play certain pieces of music.

The entire documentation, (Windows) binaries and source code and SDK are available.