I used to use Microsoft's file/folder comparison tool, WinDiff, quite a lot, but I haven't done so for years. TextDiff does more, finding & comparing some content differences, but I didn't want something that made big changes to Windows when I might not ever use it in the future. I also looked for alternatives while I was at it, hoping to pick up something portable, or 2nd best, in the Windows Store. I struck out with the store -- they had 2 apps, neither looked promising -- and looking for free apps, I found DiffMerge, WinMerge, & Pretty Diff, a web app. DiffMerge had a nag screen, so I got rid of that, and then just basically compared the impact of WinMerge & TextDiff on Windows. WinMerge has a 64-bit version which is a plus.
From a more purist point of view, TextDiff turns out to be an example of how to ruin an extremely lightweight app by using Windows Installer. I used Universal Extractor to get the app itself out of florencesoft-textdiff.msi, then ran & registered that, getting 4 new registry entries, and no additional files added. Then after deleting those 4 registry entries, starting fresh, I ran florencesoft-textdiff.msi. That time I recorded 245 new registry entries, with one new file in ProgramData, & 5 new files plus one folder in C:\ Windows\ Installer\, plus took a chance on screwing up the Windows Installer, which happens whenever you run an .msi file -- if the coder did it wrong, Windows Installer is screwed.
But again, that's from a more purist perspective. I wound up keeping TextDiff -- My Version, with the 4 registry entries -- because that was less than half the new entries using WinMerge. That said, I wasn't too picky about features since I haven't had need for this for years -- for some people WinMerge or Pretty Diff might be a better choice.
winmerge[.]org
prettydiff[.]com