Lightfeather is an open source 3D Engine for MacOSX, Windows and Linux.
It is distributed under the zlib/libpng license which allows you to use it for any purpose whatsoever including commercial projects without the need to redistribute your changes in any form or even mentioning that you use it (although that would be nice, of course).
Lightfeather started as IrrlichtNX, a CVS repository for the Irrlicht engine, in 2004.
It has since been completely rewritten and is an independent project since June 2005.
To use Lightfeather you need to be proficient in c++ programming It is geared towards intermediate to professional programmers and not towards beginners.
Lightfeather uses Mercurial instead of cvs for a few months now so the statistics are outdated.