Amazon downloader file
The Amazon downloader file is used to provide downloads in Amazon's music download store. It used to be that such downloads would be provided straightforwardly as MP3 files, but Amazon changed it to go via this intermediate file in order to push people into using their proprietary downloader, which uses the .amz file to find and download the actual music file. Somebody has managed, however, to reverse-engineer the format and create an open-source downloader in the Python language.
The format is a binary file encoded in Base64 encoding. There have been various versions, some of which encrypted the binary contents and others which forgo the encryption.