Draft license to be placed in https://github.com/VCVRack/Rack/blob/v1/LICENSE.md:
All VCV Rack source code is copyright © 2019 VCV and licensed under GPLv3 with a non-commercial plugin license exception and commercial licensing available.
VCV Rack Non-Commercial Plugin License Exception
A Plugin is defined as a software package intended to be linked and executed by this software.
You are granted the permission to use and redistribute this software’s Application Programming Interface (API) in your Plugin in source and binary forms, as well as link to this software with the Plugin, regardless of the Plugin’s license terms, provided that the Plugin is distributed free of charge.
Derived works of this software may keep or omit this Exception.
This means that non-commercial plugins do not need to be licensed under the GPLv3 and can be distributed in source or binary form under any license (open-source or proprietary freeware). However, plugins that copy a significant portion of non-API source code from Rack must be licensed under GPLv3.
Email contact@vcvrack.com for licensing commercial plugins.