Wurfel Engine is a free and open source 2.5D isometric game engine written in Java.
Wurfel Engine is licensed under a BSD3 license which means you can use it for free - even commercially.
Windows, Mac, Linux are fully supported.
Wurfel Engine uses algorithms specially designed for isometric block worlds and renders only what is visible to the player.
A powerful and efficient light engine shades the scene – vertex based or via normal map shading. Global and local light sources.
The map is divided into chunks which allows the streaming of almost unlimited world dimensions.
With the built-in WYSIWYG map editor players or level designers can shape an immersive world with immediate feedback.
Download the Wurfel Engine SDK (source, jars, docs etc.):
Download Wurfel Engine SDK
If you may be further interested in the technology used in Wurfel Engine, you can read my article on Gamasutra or my bachelor thesis (German).