[dizlexik]

I've been using WinDirStat for a tree visualization of Windows disk space for a very long time. Great software. https://windirstat.net/

[smlavine]

QDirStat is a Linux equivalent: https://github.com/shundhammer/qdirstat

[Culonavirus]

SpaceSniffer is also good (and a single exe), I keep it on all my windows machines desktops for yeeeeears

[nchmy]

Check out wiztree, which is in another comment. Orders of magnitude faster than windirstat