Source Game Engine (Valve) Irrlicht Engine - A free open source 3D engine. Mobile Game Engines: find the perfect engine for your mobile game. Cafu 3D Game and Graphics Engine. Proland. Enlighten. CryENGINE. OGRE – Open Source 3D Graphics Engine.
Let's Make a Voxel Engine. These tutorials and guides are what I wrote as I made my own voxel engine which later changed into the game Vox.
If you are interested in learning about voxel engines, or want to make your own voxel game then these articles and tutorials should help you achieve this. Please be sure to checkout Vox, the game I am making that is based on the code contained on this site. This series of guides and tutorials is going to be on the topic of making a voxel engine. If you don’t know what a voxel engine is you should probably research that first. (Voxel information) The main purpose of these guides is to introduce you to voxel engine concepts and ideas which help you produce an engine that satisfies a number of goals.
Unity. C4 Game Engine. Bitsquid. Gameplay - free 3D game engine.