~/. for Darwin, ~/Library/Application Support for macOS. That simple.
What are CLI tools that work under macOS but not under Darwin? Shortcuts like `code` or `pycharm` that open graphical apps? CLI tools that come bundled with macOS? Yeah these could use the latter.
Darwin by itself also need not come with CoreFoundation & GCD (although I believe since these are open-sourced the only darwin distribution, PureDarwin does include it).