> stacked diff workflow pioneered by Phabricator
Ahem, pioneered by gerrit. But actually, I'm almost certain even that wasn't original art. I think gerrit just brought it to git.
Gerrit was forked from Rietveld. Not sure if Rietveld or Gerrit are better though.
https://github.com/rietveld-codereview/rietveld https://en.wikipedia.org/wiki/Rietveld_(software) https://codereview.appspot.com/
To my knowledge, stacked diffs were first done in the Linux kernel as stacks of patches sent over email. From there they spread to Google and Facebook. (Source: I worked on Facebook's source control team from 2012-2018 and did a lot of work to enable stacked diffs there.)