So it was alluded to in Should we allow software questions? (take 2) that software recommendation questions are generally off-topic but as pointed out by @dmckee on neutron transport approximations for nuclear rocket modelling there is no clear policy regarding whether recommendations for physics-based software for a specific problem is considered off-topic.
General topics (ie. fluid dynamics) would become a list answer and should be off-topic. Book, and from the direction of the answers on my other question, journal recommendations about general problems are off-topic.
So is this question off-topic? Can we develop a clear policy on this?
A bit more research shows that David closed as off-topic the following recommendation questions:
but this one remains open: