DiskUsage provides a way to find files and directories on storage card which consume a lot of space. Displays diagram with directories/subdirectories proportional to their size. Source code available under free license (GPL-2)
4.0.2: Support Android Oreo (restored removed functionality)
3.7.0: - Better progress report for apps. Should display correctly the app being scanned. - Fixes for some rooted devices - Android Lollipop fixes for non-emulated storage cards - Corrected data usage information for system apps
I also have a separate debug build now for easier problems diagnostic which I send to users who ask for support.
3.6.0: Better support for storage cards on Android L+