What is public-private licensing?

Public-private licensing is a business model that open source software developers have used to support their work for decades.

Everyone is free to use public-private licensed software under the terms of a public license, usually a copyleft open source license like the GNU General Public License. Generally speaking, a copyleft license gives permission to run, change, and share the project, but not to build closed or proprietary software with it.

At the same time, the developer sells private licenses, specific to each customer, to build closed or proprietary software with the project. Fees for those licenses support the developer.