Rondo 3.1.1 for Mac was available as a free download on our application library. The actual developer of this Mac application is fracturedSoftware. The software is included in Audio & Video Tools.
From the developer:
Rondo is unique among MIDI players as it has been designed to help non-score reading musicians follow the music as it plays. Its horizontal live-playing pianos located directly over vertical scrolling note columns make it very easy to see what notes are about to play while the innovative visual track filter allows you to visually isolate a track without affecting the audio.
You may want to check out more Mac applications, such as ByteController, Melody Player or I Love Stars, which might be similar to Rondo.