Adaptive fog is a simple depth-based fog effect which combines depth-based fogging with a bloomed version of the framebuffer to fake light diffusion. It's controllable through mouse coordinates to pick the fog color from the scene. Highly configurable so you can add whatever fog type you like. Bloom is from CeeJay's bloom filter.
Updated the shader a bit: it now has a fog start parameter and the color picked by the mouse is preserved after moving the mouse and toggling off the mouse overlay so you can pick a color and use that from then on.