In the system's file explorer (Finder/Windows File Explorer). This would give me a visual outline and the ability to open any file with its corresponding app.

In the system's file explorer (Finder/Windows File Explorer). This would give me a visual outline and the ability to open any file with its corresponding app. Imagine writing a book and using folders as chapters. You could then write individual pages with different apps, say some plain text, some Word documents, a few spreadsheets, images, videos, etc.