This is not particularly ground-breaking... a little DIN-mountable MIDI interface box to connect a PC game port to some MIDI devices. In particular, the innovations on display here are the alternative 3.5" miniplug ports which may be used alternatively to the DIN connectors (but not at the same time!)
The circuit is very simple. This schematic is missing the 3.5" miniplug for the MIDI-IN port (J1), but that should be trivial to add in parallel by copying the 3.5" jack (J3) wired to the MIDI-OUT port (J2).
The latest version of KiCad files can be found at the midimbox repo.