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There is a large number of 3D engines, many of which are available for free. First a list of those I have seperate pages about:
The source code for Wolfenstein 3D was released for non-commercial use in 1995, but as far as I could find out, never under the GPL; the same goes for Heretic and Hexen.
Ken Silverman released the original Build Engine under a license of his own (2000-06-20), which is however similar to the GPL.
If you are looking for a complete authoring system, this is maybe the most interesting product now on the market. It can be used for all kinds of games, and it can be used with or without additional programming. It comes in four versions, the cheapest is only $49 while the most advanced supports multiplayer and lets you release a level editor for your game. And the engine is good.
Cube is a 3D engine for Windows, Linux, Solaris, and FreeBSD developed by Wouter van Oortmerssen and released under a license functionally equivalent to the BSD/MIT/ZLIB licenses.
Landscape-style engine that pretends to be an indoor first person shooter engine. […]
Allows in-engine editing of geometry in full 3D (you fly around the map, point / drag stuff to select it / modify it), which can even be done with multiple people at once (a first!). Has simplistic but effective fine grain vertex lighting that looks like lightmapping and can do dynamic lights & shadows. Doesn't need any kind of map precompilation, even lighting is done on the fly. Has very simplistic quad-tree world structure that can do slopes (heightfields with caps) and slants, water, does decent collision detection & physics, has client/server networking that goes a long way in giving a lag-free game experience, and features a Doom/Quake-style singleplayer and multiplayer game with some uncompromising brutal oldskool gameplay.
Most of the engine design is targeted at reaching feature richness through simplicity of structure and brute force, rather than finely tuned complexity.
Howard Wen wrote a very favorable review on O'Reilly Network.
Torque was developed for Tribes and Starsiege. It can now be had for $100 per programmer from GarageGames, support included. Once you have created a game with Torque, there are three options:
According to the (defunct) Crime Force website,
Torque has the unique ability to create large landscape environments combined with detailed interior structures such as buildings with individual rooms. To reduce polygon count, the engine features a level of detail (lod) system where each model or building can be represented by an optimized model according to view distance. This is accomplished by the 3d artist creating multiple copies of the same object with different detail levels.
Oh Lord, there are lots and lots of game engines out there. Just check out the 3D Engines list—it's huge. I'll list any here that I find that are free or inexpensive. I know nothing about them; the text, if there is any, is simply copied and pasted from the websites. You could also check out my Doom page, Editing and Enhanced Versions. Some of these ports are quite interesting engines to create your own game.
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