DirectX10 C#, Managed and Unmanaged C++ homemade 3D engine.
It was based on decimal floating point precision to handle very large universes.
Each sections (universe, galaxy, solar system, planet) were converted/scaled to float then rendered in their own camera.
All planets were procedurally generated on GPU (and also on the CPU side to handle collision).
It was a WYSIWYG environment and you could go wherever you wanted without any loading.
Grass and water only exist on the GPU side.
The atmosphere used a spherical light scattering solution with volumetric density for the clouds.
It also had: Hdr Eye adaptation, Depth of Field, Parallax mapping, vector Motion Blur, ...