Have you got some programming knowledge and dream of creating your own 3D games? If so, Crystal Space could help as its a hugely popular and free 3D software development kit (SDK) for Unix, Windows and Mac.
Crystal Space renders with OpenGL software (meaning it works with most 3D graphics cards too) and features curved surfaces, volumetric fog, dynamic colored lighting, terrain engine, LOD, procedural textures, portals, etc. Crystal Space has a graphical interface which is not actually a WYSIWYG editor but rather a collection of libraries with which you can create a 3D game.
It allows you to add special effects such as dynamic lighting, reflective surfaces, volumetric fog, particle effects and many more. If you're new to 3D modeling however, you might find Crystal Space very complicated. The installer alone requires knowledge of how to use the terminal and entering "% ./configure, % make and % sudo make install". However, the developers recommend following the full detailed installation instructions for optimum performance.
If you know what you're doing, the popularity of Crystal Space proves what a powerful tool it is.