GameplayKit is described as 'object-oriented framework that provides foundational tools and technologies for building games in iOS, macOS, and tvOS using the Swift programming language and 3rd party rendering and multimedia libraries such as SpriteKit' and is a Game Development Tool in the Development category. There are more than 25 alternatives to GameplayKit for a variety of platforms, including Windows, Mac, Linux, Android and iPhone. The best alternative is Godot Engine, which is both free and Open Source. Other great apps like GameplayKit are Unity (Freemium), LÖVE (Free, Open Source), Cocos2d-x (Free, Open Source) and Phaser (Free, Open Source).
Godot is a fully featured, open source, MIT licensed game engine. It focuses on having great tools, and a visual oriented workflow that can export to PC, Mobile and Web platforms. It is a cross-platform 2D and 3D game engine and game development IDE.
Panda3D is a game engine, a framework for 3D rendering and game development for Python and C++ programs. Panda3D is Open Source and free for any purpose, including commercial ventures, thanks to its liberal license. Go ahead and grab it here.
Pygame is a set of Python modules designed for writing video games. Pygame adds functionality on top of the excellent SDL library. This allows you to create fully featured games and multimedia programs in the python language.
One framework for creating powerful cross-platform games. The spiritual successor to XNA with 1000's of titles shipped across desktop, mobile, and console platforms. MonoGame is a fully managed .NET open source game framework without any black boxes.