DaisyDisk - Analyze disk usage and free up disk space on Mac
www.daisydiskapp.com
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
DaisyDisk scans your disks and presents their content as interactive maps where you can easily spot unusually large files and remove them to get more free space. The map gives you an overview of your data, so you always know what your hard disks are filled with.