Note: In order of Library of Congress Classification

(Q) Science (General)

(QA) Mathematics

Book Of Proof (2013) - Richard Hammack
Elementary Algebra (2011) - Francisco Javier Márquez
Mathematics For Computer Science (2017) - Eric Lehman et al. (PDF)
Stacks Project

(QB) Astronomy

Archaeology, Anthropology, and Interstellar Communication (2014) - Douglas A. Vakoch
Astronomy (1877) - Sir Robert Stawell Ball
Astronomy (1915) - Harold Jacoby
Elements of astronomy (1836) - John Hubbard Wilkins
Hubble 25: A Quarter-Century of Discovery with the Hubble Space Telescope (2015) - Dylan Steele

(QC) Physics

The Feynman Lectures on Physics - Richard P. Feynmann

(QD) Chemistry

A Dictionary of Chemistry (1777) - Pierre Joseph Macquer and James Keir
CK-12 Chemistry - Second Edition (2011) - Sharon Bewick et al.
From Vitamins to Baked Goods: Real Applications of Organic Chemistry (2012) - Kieran Gallagher and Lizhi Fan

(T) Technology

Mechanical engineering and machinery (TJ) (includes Energy Conservation)

Climate Change and the Oil Industry (2003) - Jon Birger Skjaerseth and Tora Skodvin
Our Car as Power Plant (2014) - Ad van Wijk and Leendert Verhoef
Sustainable Energy - without the hot air (2009) - David J. C. MacKay
Understanding the Global Energy Crisis (2014) - Eugene D. Coyle and Richard A. Simmons

- Sections to add

(QE) Geology
(QH) Natural history
(QK) Botany
(QL) Zoology
(QM) Human anatomy
(QP) Physiology
(QR) Microbiology
(R) Medicine (PDF)