Lightfeather is a 3D engine for Linux, Mac OS X and Windows. It is designed to be easy to use but still take advantage of the features of modern graphics hardware.
Awesome engine, that while documentation is lacking overall , and the website needs a lot of attention, the code is amazing and easy to use and there are 20 or so tutorials for your perusal . It has awesome features like paging support (* and a editor for it), animation blending ( that few OSS projects even have ) and very nice HDR and other features you will likely want for games or apps. Very nice helpful people on IRC as well, which is a big plus these days. THe engine has several ready to go apps like paging terrain editor,with splatting, GUI editor ( you can do anything), material editor and modeviewer just to name a few. You just can not beat it, for OSS I don't think. In the right hands, this engine will take you a long ways, and If you get stuck, the forum is there, but honestly IRC is going to get your answers much faster as the forum seems a bit deserted at this juncture, but they have plans on creating a new website layout with added functionality. Ive tried the current OSS engines that are out there, and this does have hurdles to jump, but its a amazing engine for the price of free ;) Give it a try, I did, and Im excited to see what Im going to create :)