Defold is a free game production platform used by developers to create games for various devices.
As of May 19, 2020, Defold is now officially open source. You can go to defold.com/opensource for all the details.
“We are happy to announce that as of May 2020 Defold, the ultimate cross platform game engine, has been transferred to the Defold Foundation and made available as an open source project! We belive this will bring transparency to the development process and we invite our community members to get involved”. – Defold Foudation