The Xenko game engine just released version 2.1. This recently out of beta C# powered game engine just got a bunch prettier with several 
rendering improvements. The engine also gained the ability to stream textures which should decrease scene load times and memory usage. The input system was rewritten and Direct X 12 support was improved.
The following is a summary of new features in the 2.1 release:
- Local reflections
- Clear coat shading
- Thin glass materials
- Texture streaming
- Render masks
- Improved profiler
- Debug text during runtime
- Rewritten input system
- Improved Direct3D 12 support
- Improved environment fresnel
- Japanese documentation now available
For more details be sure to check out the release notes which includes a full change log.
Xenko was previously known as Paradox and we did a short tutorial series available here if you wish to learn more.