In our ongoing development of Spire, we've had to build a lot of our own systems to accommodate the complexities of the game. The existing solutions in Unity are not well suited to a game with dynamic worlds. One of the biggest challenges has been writing a good-looking custom lighting system that could work well with procedural worlds, while keeping system performance in mind.
We're happy with how it's turned out — it renders nice shadows, simulates indirect lighting, and handles volumetric effects. We are releasing the volumetric lighting system on the Unity Asset Store as the first phase of hopefully sharing our whole lighting package. It's an extension of Unity's lighting — it adds real-time volumetric lighting, enabling extra depth and realism with rays of light and fog of variable density.
The system is called Hx Volumetric Lighting — the Hx is a prefix we use in our code as an abbreviation for Hitbox. You can find more information and view the documentation at hitboxteam.com/HxVolumetricLighting, and you can purchase it on the Unity Asset Store for $40 USD.