I work in a large monolith that doesn't always have the package and code separation that I'd like.
I built PackageMap to help me visualise the codebase, and see where the natural seams were -- or should be.
I use the tool to build a directed graph of the type and method usages, and to see which code is grouped into which packages. The code is rendered in a graph diagram that I can see, query, and filter. It really helps me when I'm doing code review or working on a part of the code I'm not too familiar with.