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For small values of easy: vim. (It is really easy to do I think, doing it correctly instead of just being clumsy and hitting some key that starts it, that is the challenge ;-)

I only learned now that emacs could do it.

I didn't know that vim could do this! I've always assumed that undo/redo (u/^r) were my only options.

For anyone else who didn't know, try ":help undo-branches" or take a look at https://vim.fandom.com/wiki/Using_undo_branches , which has a simple example of use.

Emacs branching got way better with undo-tree, check it out :-)

GIMP.

This is one thing it does very well, it beats emacs hands down in history visualization (at least without undo-tree, I've never tried it).