Defold uses LuaJIT which is itself really fast. The source code of the engine is all public on GitHub if you need to modify something yourself. Defold is the complete solution for creating multi-platform games (HTML5, Switch, Android, iOS, Windows, Linux, macOS).

With Defold, I can develop a game and export it to all platforms without changing any code. We do not even have to bother about the conventional system items such as directories, graphic forms, input methods, processes rendering, network functions, or so on. It normally takes only a few seconds to create Defold 2D or 3D animation. You may also send content and gameplay logic to updates on your PC, mobile or controller to an existing running game.