ZAP Media Player is able to play MIDI files. Musicians mainly used them, and the main characteristic of  MIDI files is their small size, however the audio quality is usually poor when you don't have a complete midi studio.

Contrary to WAV, WMA, MP3 and OGG, a MIDI file doesn't hold any sound but instead a kind of score with information on the way each note must be played by the electronic components of the sound board. For this reason the audio quality of MIDI files vary from one computer to another due to the intrinsic quality of the soundboard being used. Finally a MIDI file is unable to reproduce human voice but just musical instruments.