GodRays is one of my favourite toys Nuke has to offer and sometimes I end up doubling up the effect in various counter-transform operations.
BidirectionalGodRays is a combination of either double-stacked GodRays nodes or a pre-transform with a singular godrays node.
You can find the example on lens astigmatism here
You can download the tool here
You can revisit ChromaticBlink here