Spyglass is described as 'perfect companion for fixing your cluttered disks and folders. It allows you to navigate your folders and files using a beautiful Sunburst View, a versatile File Navigation View, and smart Breadcrumbs' and is an app in the OS & Utilities category. There are more than 10 alternatives to Spyglass for a variety of platforms, including Windows, Mac, Linux, BSD and Electron / Atom Shell. The best alternative is WinDirStat, which is both free and Open Source. Other great apps like Spyglass are Baobab Disk Usage Analyzer (Free, Open Source), DaisyDisk (Paid), Space Radar (Free, Open Source) and crossdirstat (Free, Open Source).
Baobab Disk Usage Analyzer is a graphical application to analyse disk usage in any Gnome environment. Disk Usage Analyzer can easily scan device volumes or a specific user-requested directory branch (local or remote).
With DaisyDisk you can free up disk space by quickly finding and deleting big, useless files. The program scans any mounted disk and displays it on the sunburst map, where segments mean files and folders, proportionally to their sizes. The map is easy to read and navigate.
Free open-source cross-platform file & directory statistics as found on Github - Generate a directory tree for any given folder - View any folder as colored rectangles (squarified algorithm) - Customize the rectangle colors and show statistics about filetypes - Export...