Real-time 3D visualization of space
Celestia is an application for real-time 3D visualization of space, with a detailed model of the solar system, over 100,000 stars, more than 10,000 galaxies, and an extension mechanism for adding more objects.
Photonix is a 3D Modeling and Rendering Tool that have intentions to reach 3D Max to produce Realistic Images using Photon Mapping
Atomic Game Engine (AGE) is a hardware accelerated 2D/3D game engine to develop advanced 2d/3d games. Now, it is just a 2d engine. more information will be available in the next version.