This is not my area of expertise, but typical alternative formats would be Braille and audio. They're some of the ones that might be more understood. More recently, in the last 20 years or so, e-text has been, potentially, a really revolutionary alternative format. There are screen readers. I'm using one on this Mac right now to access the text I wrote for my presentation. We can access electronic books using these technologies.
The issue occurs when DRM is put on e-books. For Kindle, or in the NOOK store from Barnes & Noble, DRM can limit the ability of screen readers to access the materials, so we become locked out of a potentially accessible book.