[wting]

For those that use vim, gundo.vim visualizes the "undo-tree" and allows you to preview / jump to any revision: https://github.com/sjl/gundo.vim

[srik]

There's a fork called mundo which has an inline diff mode that I'm a big fan of — https://github.com/simnalamburt/vim-mundo

[caymanjim]

Came here to post this. The undo tree is actually built into Vim, but I didn't know about it until I discovered Gundo a decade or so ago. I rarely use it, but it's still installed and has saved me hours of work on a few occasions.