Mac Audible Downloader & Converter

I'm seeking a Mac-compatible software that can download audiobooks from Audible and convert them into different formats.

Key Features:
- The ability to download audiobooks from Audible
- Conversion of downloaded files into various formats

Ideal Skills and Experience:
- Proficiency in Mac software development
- Experience with Audible's platform and its download protocols
- Knowledge of audio file conversion and various audio formats
- Strong understanding of user-friendly interface design