LITIengine is a free and open source Java 2D Game Engine. It provides all the infrastructure to create tile based 2D games with plain java, be it a platformer or a top-down adventure.
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Pro Easy to use
Clean and well-designed API that is easily discoverable. Comes with a simple tool (utiLITI) for editing levels based on .tmx maps.
Pro Free an open-source
The engine is published under the MIT license and is entirely free to use.
Pro they are developing a beta for mac and linux
Pro Active and helpful community
Has an active forum and discord channel to discuss topics about the engine.
Con Limited to Desktop
Games made with the engine only run on Windows, Linux and MacOS. There is no support for Android or HTML, yet.