QGroundControl (QGC) is dual-licensed as Apache 2.0 and GPLv3. All contributions have to be made under both licenses (see CONTRIBUTING).
The Apache 2.0 License is a permissive license which allows QGC to be built and used in any environment, including proprietary applications. It allows QGC to be built for mobile app stores. When building with Apache 2.0 a commercial Qt license is required.
The GPL v3 License is a strong copyleft license. When building QGC under this license the open source version of Qt can be used. Our licensing grants the permission to use a later version of the license, however, contributions have to be made under 3.0.
If you have questions regarding the licensing, please contact the maintainer Lorenz Meier, [lm@groundcontrol.org].