GrandPerspective

Every few months a Mac fills up and nobody knows why. GrandPerspective answers that in one scan: point it at a volume, wait, and you get a rectangle per file, sized by bytes. The 12 GB virtual machine you forgot about, the folder of camera originals, the Xcode caches — they are the large shapes, and depth in the folder tree stops mattering.

What it does better than the polished commercial tools is remember. You can save a scan to a file and load it later, then compare it against a fresh one to see what grew. That is the feature you want when a disk is filling up by a gigabyte a week and you cannot tell what is doing it.

The trade is presentation. The colours are flat, the controls are plain, and reading a dense treemap takes a moment of learning that a prettier app would have smoothed over. If you scan your disk twice a year and want the experience to be pleasant, a paid alternative is worth the money.

The App Store version costs $2.99 and is the same code. Buying it is a tip to a developer who has kept this alive for two decades, not a feature unlock — take the free download without guilt if you prefer.