The Fiddler 4 installer thinks there's something still installed in c:\Program Files (x86)\Fiddler2, but that folder no longer exists and the old version of Fiddler is no longer listed in "Programs and Features".
Error message when I run the new version:
"Machine-wide Progress Telerik Fiddler installation has been found at C:\Program Files (x86)\Fiddler2\ . Please, use that one or uninstall it before starting the per user Fiddler installation."
The offending folder does not now exist. "c:\Program Files (x86)\Entity Framework Tools" exists. "c:\Program Files (x86)\Google" exists. There is nothing between them. They are adjacent in the directory listing.
Now Filddler 4 runs.
But if I hadn't still had the old installer lingering in my downloads folder, I would have been out of luck. Please fix.