Macchiato is a MIDI file processor.
It takes a MIDI file, transforms it using rules, and outputs another MIDI file with the specified modifications.
This is useful to enhance a MIDI file, for instance produced by a score writing tool (e.g. MuseScore), by adding some humanization procedures and any other more-or-less fancy enhancements (to taste!)
It is used for instance by Rex Potam for his songs and other musical works.
For more details, please refer to the wiki.