Not a "Web App" as such, but a simple utility script for Windows computers. It makes a copy of all the files in a folder into a set of sub-folders named according to date. Files are copied into the folders corresponding to their file dates.
This is expecially useful for copying large numbers of photographs in a single folder, and sorting them into separate folders by their capture date.
Download the file at the link, and place it in the folder which you would use to store your newly copied pictures (the "mother folder"). Then double-click on the file. You should then see a number of new folders appear, named like dates: YYYY_MM_DD. (This naming format allows the folders to sort alphabetically). A text file is created, showing a list of all the files copies and where they were put. The folders will contain copies of all the files in the "mother folder" (including the script file and the newly-created text file).
Once you are happy that all your files are safely copied, you can delete the originals from the "mother folder".