If you don't know what humble bundle is, its a charity site that sells a bundle of (digital) things (usually 4-5 items, and usually games) on a name your price system ($1 minimum), and if you spend more then a certain amount (usually between $5 and $6) you get 2 or 3 more items added on. And you can choose who gets the money and how much (usually you can choose the charity, which changes each time the bundle changes, or the company/developer/etc providing the content, or can split the money however you want).
The main bundles change every couple weeks and they have a weekly bundle as well (generally different from the main one)
This time they are offering up to 8 audiobooks from various authors. With the charities being The Electronic Frontier Foundation, and World Reader.