These files (sourced from
here) can be opened in anything that can work with MIDI (such as MuseScore, Sibelius, Logic Pro, Music21 etc.) and easily converted to MusicXML. This format makes them really useful to explore different questions related to music analysis. Also note that I am currently (thru 2022) in the process of creating a database of MusicXML files of Nikolai Kapustin's works which I will post here soon.