• https://github.com/i-rinat/fragview
• http://davtools.sourceforge.net/#screenshot

Not supported. Duplicated files can be removed and hardlinkied using 3rd party software:

• rdfind is a program to find duplicate files and optionally list, delete them or replace them with symlinks or hard links;
• jdupes - can convert duplicate files in hardlinks or relative softlinks
• fslint - GUI tool (deprecated)
• fslint-unofficial - snap provided but doesn't work!
• rmlint
  • Nice feature to save state: replaying
  • Can save checksums to xattr for faster consecutive runs miscellaneous-options

Not for ext4:

• duperemove

rmlint /BIG/POOL --progress --xattr -c sh:hardlink --size 1M

Tools doesn't touch filesystem. It generate rmlint.sh to make desired modification. Please review script, especially function cp_hardlink. Function needs to hande errors a bit better - it first removes file without backup, and then if error occurs during hardlink there is no way back.

rmlint.patch

1c1
< #!/bin/sh
---
> #!/bin/sh -eu
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>             mv "$1" ~"$1".rmlint.$$
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>             rm ~"$1".rmlint.$$

rdfind . -dryrun