Mac only: We've all experienced full hard drives, but figuring out where all your hard drive space has gone is never easy. Freeware program OmniDiskSweeper easily shows you which files and folders are taking up space so you can free it up.
OmniDiskSweeper is different to other disk space utilities for Mac: there are no graphical representations and no multiple windows to sort through. Just an organised list of the biggest folders on your hard drive.
When you first start it up, you choose which disk you want it to scan, and when it's done it shows you a column view of every accessible folder and file on that drive, organised and colour-coded by size. You can delete the space-eating files and folders from inside the app, and it will recalculate the sizes right then and there for you. (Note: If you delete from the program, the files do not go into the trash — they are immediately deleted.) The app will also let you know if something is a system file or folder so you don't delete anything important.
If you want something that is fast and simple you can't go wrong with OmniDiskSweeper. And, along with many other utilities offered by The Omni Group, OmniDiskSweeper is now free, so there's no reason not to give it a whirl.
OmniDiskSweeper is a free download, Mac OS X only.