Storage space

Automatic cleaners

BleachBit

An open-source, cross-platform program available on Linux and Windows. Can clean system and application files. To keep it simple, here's a short list of some of the stuff it can clean: Discord, Google Chrome, Firefox, Thunderbird, VLC, trash, cache, custom directories and more.

• Arch Linux repositories
• Nixpkgs
• Winget
• Other

Tree visualisers

See how many % each folder takes up.

Treesize

Treesize is a freemium, Windows-only, program. It features a decent-looking GUI and is available on the MS Store for automatic updates.

• Winget
• MS Store

gdu

GDU is an open-source and cross-platform TUI program. It is fast and quite intuitive, if you're not afraid of the terminal. Find a package for your system (including Windows) here.

• Arch Linux repositories
• Nixpkgs
• Homebrew formula
• Winget
• Other

Alternatives to gdu

You might already know alternative such as ncdu and these are very similar tools. I decided to put priorities gdu here, as it is signifficantly faster than the alternative I've tried, especially on an SSD. See some (possibly biased) comparisons here.