WinDirStat scans a drive and shows where space goes using a directory tree alongside a colourful treemap, where each rectangle is a file sized by how much room it takes. It makes finding and clearing space-hogging files fast and obvious.

Highlights

Treemap makes large files instantly visible
Completely free and open source
Lightweight, no account or telemetry
Delete straight from the results

Watch-outs

Dated interface
Initial scan is slow on very large drives
Windows only

Good for

Reclaim disk space

WinDirStat is a single-job utility that does that job well: the treemap turns "my disk is full" into an obvious answer in a couple of minutes. The UI is ancient and big scans take a while, but for free, offline, open-source disk visualisation it remains the default on Windows.

When to use it

windows_users_reclaiming_space
open_source_advocates

Avoid if

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need_cross_platform

Free

Free tierOpen source

Free and open source (GPL).

Open source
Native
Offline support
Native

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WinDirStat

Highlights

Watch-outs

Good for

When to use it