Rendology is a Glium-based 3D rendering library. It is not, however, a game engine.
There's a blog post on Rendology's architecture.
Rendology features amateur-grade implementations of:
- Shadow mapping
- Deferred shading
- A glow effect
- Instanced rendering
Each of the rendering effects can be turned on and off separately.
Rendology makes it easy to integrate custom scene shaders into the rendering pipeline.