DaisyDisk is a disk space analyzer for Mac OS X. For alternatives, see here.
Ranked in these QuestionsQuestion Ranking
Pro Helps find and delete files taking up HDD space
While working on your Mac you create and download a lot of files, but rarely delete anything. As time goes by you have less and less room for your data. DaisyDisk finds those hidden unused gigabytes.
Pro Awesome visualization of files on drive
DaisyDisk gives you a perfect overview of all the disks connected to your Mac, be it Macintosh HD, flash card, Thunderbolt disk or network storage. And does it in a beautiful way.
Con Expensive for how often it is used
Con Calculation based on 1000 not 1024
It's nice to have a base 1000 (MB, GB, …) calculation but it should be optional. Default should be 1024 (MiB, GiB, …)