The Directory of Open Access Books

As the name suggests, there is a relationship with the Directory of Open Access Journals and as the name further suggests it's a directory of free full-text academic e-books, and its main purpose is to improve the visibility and discoverability of open access textbooks.  I've no idea if it's of any use to you, but it's certainly worth a look and of course new titles will be added all the time, so even if you can't find anything you want to peruse, you can try again at a later date. As I type, the directory contains links to 756 books, but that number will only increase  Go here to have a look.