The holy grail of a stacked diff workflow would be making multiple Github PRs each made against the previous branch instead of trunk, and then updating the branch that's closest to trunk and rebasing all of the children PRs without having to force push into any of them.

Git and Github do not support this workflow directly, and this creates space for all the other tools.

Jujutsu comes close to supporting this workflow directly, without having to provide any specialized utilities that mention "stacked diffs" at all.

https://github.com/spacedentist/spr (not to be confused with ejoffe/spr) is a utility that maps a local change to a remote branch, updating the branch (without force pushes) when the local change is updated. (Changes work the same as they do in JJ, but the implementation is different.) And this works even when you have a stack of changes and update one in the middle of the stack.