For Mac - Disk Inventory X
Finding hard drive hogging files isn't always easy once you've checked off the common offenders. While you might argue that with hard drive capacities being what they are today(friggin huge), why care if your 3TB hard drive has 1Tb of crap on it. Well the argument is this. Moving to a Solid State Drive, you will not be as spoiled as you once were. WinDirStat was awesome was mechanical drives were smaller and it still awesome with smaller SSDs.
Super simple to use. Tell it to scan the drive and it will give you a file tree as well as a visual representation of the files on the drive. You can even right click and go to the file, or delete the file from within WinDirStat!
It is opensource, but if you find it useful or have used it for any years, I urge you to donate to their work!