FreeMIDI is a complete MIDI operating system for the Macintosh. Its parts include a FreeMIDI system extension, an optional OMS (Open Music System) emulator extension (to emulate the Opcode MIDI System), and a FreeMIDI folder that resides in the top level of the System folder.

FreeMIDI automatically detects which type of MIDI interface is connected to your Mac's modem and/or printer port, determines which MIDI devices are connected to the interface (it recognizes more than 200 device types), and provides users with a System 7 style graphical representation of their MIDI studios.

FreeMIDI also provides pop-up sound lists for more than 100 popular MIDI synthesizers, as well as generic support for any general MIDI device.

FreeMIDI even includes advanced features such as interapplication communication, real-time synchronization, multiple-application, and support for Digidesign's SampleCell NuBus card.