CNET's Download.com offers several free midi players that service a variety of operating systems. In addition, the site offers several other midi-related pieces of software, including converters and visualizers.
Most of the midi players available at Download.com contain a number of different programs, which allows users to play different instrument tones for each part. In addition, these programs allow the manipulation of midi notes, making it possible to adjust the pitch, timing and velocity of the note. These powerful programs make both listening and editing midi files possible, and most audio producers use them heavily as a part their work flow.