A long time ago, I covered MuseScore, an application that can typeset your music as well as play it back.
And now, for something completely similar…
Originally developed as a game to train people how to play piano, Synthesia is equally adept at playing back your music. Instead of a bunch of notes on five-line staves, Synthesia uses a Guitar-Hero-esque approach, by translating notes in a MIDI file into colorful falling bars that strike a keyboard. The advantage of this visualization is that everyone, including non-musicians, can understand what’s going on in the music.
Take a look at the videos below:
Try it out
Synthesia has a free version, and a Learning Pack that extends its capabilities. For most users, though, the $25 upgrade isn’t necessary to enjoy all the great features it already has.