Crystal Space
Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. It supports: true six degree's of freedom, colored lighting, mipmapping, portals, mirrors, alpha transparency, reflective surfaces, 3D sprites (frame based or with skeletal animation), procedural textures, radiosity, particle systems, halos, volumetric fog, scripting (using Python or other languages), 8-bit, 16-bit, and 32-bit display support, Direct3D, OpenGL, Glide, and software renderer, font support, hierarchical transformations.

The OGRE Team OGRE 3D rendering engine
OGRE v1.0 is the leading open source real time 3D rendering engine. OGRE is packed with features to make your development life easier, whether you're making games, architectural visualisation, simulations, or anything else which requires a top-notch 3D rendering solution.

caligari gameSpace Light
gameSpace Light is not just a trial copy of gameSpace, but a functional package in its own right. Now you can work on models using all the modeling and animation tools from gameSpace, and save models of up to 650 polygons so that you do not have to do everything in one go. You can save to standard gameSpace format, and industry standard .X format, so your can use your models in your games and mods! gameSpace Light is designed to let you get started in creating 3D content for games, so you can find out if it is for you, get a head start in learning about 3D modeling and animation, or even start creating your game or a game prototype, all without the need to worry about cost.

Mark Overmars Game Maker
Did you always want to design computer games? And you don't want to spend a lot of time learning to become a programmer? Then you came to the right place. Game Maker is a program that allows you to make exciting computer games without the need to write a single line of code. Using easy to learn drag-and-drop actions you can make professional looking games in little time. Games with backgrounds, animated graphics, music and sound effects. And once you get more experienced there is a built-in programming language that gives you full flexibility. What is best, Game Maker can be used completely free of charge. And you can use the games you produced in any way you like. You can even sell them! Game Maker comes with a collection of freeware images and sounds to get you started. Also there are a number of example games. These are mainly provided as examples and not as full-blown games. Here you see a picture of the interface.

AwingSoft Light Map Maker
Light Map Maker is a tool for real-time 3D developers, it's main feature is adding realistic lighting to real-time 3D scenes. It's robust lighting utility support ray tracing lighting, realistic radiosity lighting, and caustics, mirror, ... Light Map Maker provides a SDK(c++) for importing/exporting various data; now supports some popular 3D formats; so it's compatible with most game development software.