The .M4B format is for audiobooks and in this case, includes both an image and direct access to all sections of the audiobook.
Android
For Android devices, we recommend the free Sirin app.
Apple-Mac computers
In the Apple world, i.e. macOS, the .M4B file can be played with the Apple Books program.
Apple-iPhone, iPad, iPod Touch
For iOS (iPhone, iPod Touch) and iPadOS (iPad) we recommend the free BookPlayer application.
Windows
For Windows 10 and Windows 11, we recommend the free Audibly app. It is available for free in the Microsoft Store.