ADirStat is a treemap visualisation for your android storage usage. It shows a similar view to KDirStat (Linux) and WinDirStat (Windows).
Large files and directories can easily identified, even if they are deep in subdirectories. Unneeded files can be quickly deleted or inspected further.
ADirStat is published under the MIT licence, and code can be found on GitHub: https://github.com/FlightOfStairs/ADirStat