You may freely distribute Terra3D and use the source code for research, or even pieces of it in your own program. If you do use my code in your own program, please give me credit. - Steve Wortham
Terra3D combines some more advanced techniques than my Abyss program and is a much better demonstration of a modern terrain engine.
Features:
multi-textured terrain and water with a pre-rendered lightmap produced by raycasting
configurable number of triangles for the terrain
an F14 model
a particle engine designed for a glowing exhaust effect
a glowing sun effect
a sky dome with a fading horizon
flowing water
Requirements:
P300, 64MB, with a decent video card that supports OpenGL.