HerMIDI is a MIDI interface for the Commodore 64 made by Hermit. The devices has only a few components and you can built it yourself. The schematics, firmware and PCB are available. The device works together with the SID-Wizard program.
Hermit also released a update for SID-Wizard. Changes in this version: MIDI-in, 2SID (stereo), 324 new instruments, new "Bare" player, Sound-FX support, and much more.

SID-Wizard v1.5