It's a thing that lets anyone run a streaming radio station, with just a folder of MP3s. Put those MP3s in an Amazon S3 bucket, and give your friends the S3 FM link.
Under the hood, the site grabs the file listing from your Amazon S3 bucket, selects the MP3s, shuffles them into a random order and feeds them to the listener. Simple.
An important note - it's your bucket, and Amazon will charge you for the bandwidth. But the good news is that it's $0.150 per GB, which means that you could transfer about 1000 minutes of audio for 20p.
And that's it. Have a go, and let me know if it breaks.