ProcessWire is a pure open-source CMS that uses a business friendly Mozilla Public License.
ProcessWire 3.x primarily uses the MPL 2.0 license, but also designates some files as using the MIT license. Both are business friendly and do not require you to maintain the same license for your own original code/files. Regardless of ProcessWire version, 3rd party modules, templates and site profiles may use different licenses at author discretion.
Third party libraries used by ProcessWire specify their own compatible license in file headers or in a LICENSE.* or README.* file present in the same directory. Files native to ProcessWire that to not indicate license in file header or in the directory can be assumed to be MPL 2.0.
MPL 2.0 LicenseMost files in the ProcessWire core source code use the Mozilla Public License, version 2.0.
MIT LicenseSome specific components in ProcessWire core use the MIT license (where specified).
3rd party filesThird party files may in ProcessWire may specify their own license. This page contains more details.
CLAProcessWire Contributor License Agreement (CLA), based on the language from the GitHub CLA.