Download of GI20Editor 2.1 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. The program lies within Audio & Video Tools, more precisely Editors & Converters. The actual developer of this Mac application is Amedeo Farello.
From the developer:
GI20Editor is a software editor for the Roland GI-20 GK-MIDI guitar interface. Besides being an alternative to programming the device through a knob, GI20Editor can greatly enhance the guitar/synthesizer connection experienced through the GI-20. With this tool, you can view and modify all system and patches parameters easily. You can save complete GI-20 setups as documents, for backup purposes and fast switching between different configurations.
You may want to check out more software for Mac, such as Aiseesoft WMV Converter for Mac, which might be related to GI20Editor.