A wide variety of authors and publishers are choosing to publish books "openly." This means they are free to access and usually have some sort of Creative Commons License.

You can access these particular books through a variety of platforms, each one looks slightly different. Try clicking a variety of links and usually you can find a way to fully read and download these books. 

OAPEN: online library and publication platform

• The initial page allows you to download or view the book
• There are no limits to downloading or printing these books