For Windows users looking to save space, there's Compactor[1] that uses the NTFS built-in compression opportunistically for only those files that benefit from it. It is not a deduplicator but the basic idea is the same: take an underutilized OS feature and make it usable.

Pretty handy when your flight sim game takes 1.2 terabytes with most of that being sparse terrain mesh data and uncompressed textures. Compressing the whole directory would take over a day according to Microsoft and their infamous progress bar; Compactor gets it done in fifteen minutes.

[1] https://github.com/Freaky/Compactor