Toxygen is the first Tox client with plugins support. Plugin is Python 3.5 - 3.6 module (.py file) and directory with plugin's data which provide some additional functionality.
Check Plugin API for more info
Toxygen comes without preinstalled plugins.
- Put plugin and directory with its data into /src/plugins/ or import it via GUI (In menu: Plugins => Import plugin)
- Restart Toxygen or choose Plugins => Reload plugins in menu.
WARNING: It is unsecure to install plugin not from this list!