How does it differ from existing tools kinda do exactly same, like e.g. toolbx. (And to a slightly lesser degree flatpack, snap, etc.)?

And what prevented adopting/supporting existing projects, instead of further tool ecosystem fragmentation? (kinda the same question, just differently phrased)

Ha! I wrote the first commit to CoreOS's toolbox in 2014: https://github.com/coreos/toolbox/commit/dc4aa0b14bceafd6afa...

And then I read your comment and my first reaction was, oh, they typoed toolbox. But, nope, Red Hat created toolbx which confusingly has the CLI binary of `toolbox`: https://containertoolbx.org