Audio books are actually books that you purchased online, just that instead of reading it, it actually 'reads' to you. They can come in the form of cassette or cds. Whether it is a new concept or not that I do not know, but it certainly sounds interesting doesn't it? For the first time, instead of reading, you can listen to the author speak.
Currently, most websites do not have downloadable free audio books. In other words, you have to purchase the cassette or cd online and they will have it mailed to your house. But base on my understanding, not every book comes in an audio book type. It is only certain books and even so, it may be a much summarised version of the actual type.
One example is Robert's Kiyosaki audio cassette, where in it, he will
give you a summarised version with a bit of extra information here and
there based on the actual book. Then,
there is another type where it comes free with the book you buy from him.
Just go to his company's website, and you'll be able to hear his 'audio
book' for free.