Armory Is A Very Promising 3D Game Engine With Full Blender Integration
The Armory 3D game engine offers complete Blender integration for essentially being able to build games in full via Blender. Armory also relies upon the Kha multimedia framework and Haxe tool-kit for delivering a cross-platform and performant experience. The renderer for this engine is based on Blender's Cycles nodes and is physically-based, supports an HDR pipeline, and can handle other modern 3D features.
I just learned of Armory this week by a Phoronix reader (thanks Martin!) and while the game engine is still in its early stages, its early work is quite promising for a game engine at "v0.1" of its lifecycle.
Those wishing to learn more about this Blender-focused game engine can do so at Armory3D.org. The code for this game engine is hosted on GitHub.