game engine

You've probably found this, but for the benefit of others I'll just put what I found out from Wikipedia.

Open sourced engines:

#-Link-Snipped-# - A lightweight next-generation graphics engine
<a href="https://en.wikipedia.org/wiki/Irrlicht_Engine" target="_blank" rel="nofollow noopener noreferrer">Irrlicht Engine - Wikipedia</a> - Another well known graphics engine under the zlib license
<a href="https://en.wikipedia.org/wiki/OGRE_3D" target="_blank" rel="nofollow noopener noreferrer">OGRE - Wikipedia</a> - A well known LGPL graphics engine
<a href="https://en.wikipedia.org/wiki/Dim_3" target="_blank" rel="nofollow noopener noreferrer">Dim3 - Wikipedia</a> - although not well-known and developing is macintosh-only, games can be played on Mac, Windows and Linux. Very easy and fast engine if used right.
<a href="https://en.wikipedia.org/wiki/Open_dynamics_engine" target="_blank" rel="nofollow noopener noreferrer">Open Dynamics Engine - Wikipedia</a> - A cross platform physics engine used in many commercial games.

<a href="https://en.wikipedia.org/wiki/Game_engine" target="_blank" rel="nofollow noopener noreferrer">Game engine - Wikipedia</a>