PlayN is described as 'cross-platform game library that allows you to create a single Java codebase that runs in HTML5, Java, Android and Flash' and is an app in the Development category. There are more than 25 alternatives to PlayN for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and iPhone. The best alternative is Unity, which is free. Other great apps like PlayN are Unreal Engine (Freemium), GDevelop (Free Personal, Open Source), Wick Editor (Free, Open Source) and CRYENGINE (Free Personal).
Unreal Engine is a professional suite of tools and technologies used for building high-quality games across a range of platforms. Unreal Engine’s rendering architecture enables developers to achieve stunning visuals and also scale elegantly to lower-end systems.
GDevelop is an open-source game making software designed to be used by everyone. Any kind of 2D games can be created with it and no programming skills are required to get started. Logic of games are made using visual events.
The Wick Editor is a free and open-source tool for creating games, animations, and everything in-between. It's designed to be the most accessible tool for creating multimedia projects on the web. Your creations can run on any device with a web browser - that means mobile too.
Open 3D Engine (O3DE) is an Apache 2.0-licensed multi-platform 3D engine that enables developers and content creators to build AAA games, cinema-quality 3D worlds, and high-fidelity simulations without any fees or commercial obligations.
Cocos Creator is a complete package of game development tools and workflow, including a game engine (based on Cocos2d-x), resource management, scene editing, game preview, debug and publish one project to multiple platforms.