OGRE is a scene-oriented, flexible 3D engine written in C++ designed to make it easier and more intuitive for developers to produce games and demos utilising 3D hardware. The class library abstracts all the details of using the underlying system libraries like Direct3D and OpenGL and provides an interface based on world objects and other intuitive classes.
The latest stable release is v1.10.4. For more information see:
Currently only the legacy GL RenderSystem is able to pass all VTests from the suite. This is partly due to the tests relying on Cg which the other RenderSystems do not support. Still it is considered the gold standard. See below how the GLES2 and GL3Plus RenderSystems behave in comparison:
If you want to dive deeper into the OGRE ecosystem here are your options.
There are 2 books written on OGRE
Beneath the OGRECave umbrella you can also find some useful OGRE Add-Ons like