Mac: When you start running out of space on your Mac, the best way to figure out where it has all gone is to use a disk space analyser. DaisyDisk, one of our favourite disk analysers, is on sale for only $5.49, down from its usual price of $10.49.
While there are plenty of excellent free options out there -- including the popular Disk Inventory X -- DaisyDisk is well designed and easier to read.
Even if you don't need it right now, it's a good app to have around for the inevitable day you run out of hard drive space. Hit the link to check it out while it's on sale.
DaisyDisk [Mac App Store]