Can you describe what you're trying to do better? Is it your open source code and you want to know who's using it? Or is it your closed source code and you want to know the licensing of everything you're using?
Bugs and symbols. There's a mac command line tool I can't remember the name of that pulls all the readable (and more) text from an application, this has been used to find out what made a closed source app (e.g. private iOS apis).
There are also tools which are platform specific. On macOS, for e.g., the Mach-O format can be disassembled by `otool`, for objective-c projects (and maybe Swift) you can use `class-dump`