The ADDON file extension is used by the Windows operating system. It is associated with the CFS Console Add-on Format. ADDON files store add-ons for the CFS Console utility by Zaplots. The add-ons contain components that execute when CFS Console runs. The components add custom features to CFS Console. The ADDON extension is for plugin files. When Windows does not recognize the ADDON extension, it asks to select an app to open the file. An app associates file types with addons. Opening an addon requires a program that handles the file. Zaplots developed the CFS utility to install its programs. The utility uses addons for extra features.