Ultimately, make represents a dependency graph; Something that a shell language is not well prepared to represent. Yes, it's doing X, Y, and Z at the same time,

Ultimately, make represents a dependency graph; Something that a shell language is not well prepared to represent. Yes, it's doing X, Y, and Z at the same time, but when X is done it can launch A and B, when Z finishes then C can also be started, but you don't want to run them all at the same time because of a max subprocesses limit. You don't know if X or Z will finish first, so you can't just launch C as soon as Z is done, nor do you want to waste time waiting for A and B to finish to launch C if Z is done. How do you express that in pure shell?