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Find every file and move it to current directory.
You WILL have problems if the files have the same name.
Use cases: consolidate music library and unify photos (especially if your camera separates images by dates).
After running the command and verifying if there was no name issues, you can use
ls -d */ | sed -e 's/^/\"/g' -e 's/$/\"/g' | xargs rm -r
to remove now empty subdirectories.