Moonbase

Here are four Open Source 3D engines:

1. Ogre3D – LGPLed, OpenGL/D3D
2. Irrlicht – ZLIB-licensed, OpenGL/D3D
3. Sauerbraten – ZLIB-licensed (plus restrictions on sample content), OpenGL
4. Crystal Space – LGPLed, OpenGL

Most have rudimentary physics support. For more sophisticated rigid body physics, it should be possible to integrate them with one of the open source physics engines, among which are:

1. Bullet – ZLIB-licensed
2. Open Dynamics Engine – BSD-licensed

There is also OPAL, which is a somewhat physics-engine-neutral wrapper around other physics engines, providing high-level features like motors, sensors, joints, etc.

So, the next time you need an engine for an interactive 3D project, have a look at this list and ask yourself whether you really need to license a proprietary one.

Update: a reader also points out Apocalyx, a GPLed 3D engine based on OpenGL. The GPL (versus LGPL) license might be a problem for non-GPLed projects, but GPLed projects may find it useful.

Update: We’ve got rendering and physics covered above, but it’s probably also worth hightlighting OpenAL, an LGPLed library for 2D and 3D audio, which has been used by a number of well-known commercial games.