You can read
and download,
free, 9,526 high-quality ebooks. Most of the books are the in the STEM (
Science,
Technology,
Engineering, and
Mathematics ) subjects (i.e. the "hard" sciences).
These are high-quality books, published, at least for the most part it seems, by the National Academies of Science (
nap.edu).
The
free books from NAP are all, as far as I can tell, in the PDF format. Note that NAP also
sells most, at least, of same titles, in both dead-tree (hardcopy) form, and in non-PDF ebook formats.
The
free ebooks are comprised of titles 1) released in the last 30 days, 2) titles that are probably comparable to "backlist" titles of traditional publishers, and 3) a very interesting grouping that the
NAP calls "archive" titles.
I, and probably others, have posted information in the past about the
freebies available from NAP. However, some of us may have forgotten about them; too, there are no doubt quite a number of people who have signed up for MobileRead since the last time that this treasure-trove was mentioned.
The NAP website is better explored, than being something for someone to tell you about, in my opinion. So, I'll leave the information with you . . . .