These 60+ books are free (May 2020):
The Elements of Statistical Learning
Trevor Hastie, Robert Tibshirani, Jerome Friedman
http://link.springer.com/openurl?genre=book&isbn=978-0-387-84858-7
Introductory Time Series with R
Paul S.P. Cowpertwait, Andrew V. Metcalfe
http://link.springer.com/openurl?genre=book&isbn=978-0-387-88698-5
A Beginner’s Guide to R
Alain Zuur, Elena N. Ieno, Erik Meesters
http://link.springer.com/openurl?genre=book&isbn=978-0-387-93837-0
Introduction to Evolutionary Computing
A.E. Eiben, J.E. Smith
http://link.springer.com/openurl?genre=book&isbn=978-3-662-44874-8
Data Analysis
Siegmund Brandt
http://link.springer.com/openurl?genre=book&isbn=978-3-319-03762-2
Linear and Nonlinear Programming
David G. Luenberger, Yinyu Ye
http://link.springer.com/openurl?genre=book&isbn=978-3-319-18842-3
Introduction to Partial Differential Equations
David Borthwick
http://link.springer.com/openurl?genre=book&isbn=978-3-319-48936-0
Fundamentals of Robotic Mechanical Systems
Jorge Angeles
http://link.springer.com/openurl?genre=book&isbn=978-3-319-01851-5
Data Structures and Algorithms with Python
Kent D. Lee, Steve Hubbard
http://link.springer.com/openurl?genre=book&isbn=978-3-319-13072-9
Introduction to Partial Differential Equations
Peter J. Olver
http://link.springer.com/openurl?genre=book&isbn=978-3-319-02099-0
Methods of Mathematical Modelling
Thomas Witelski, Mark Bowen
http://link.springer.com/openurl?genre=book&isbn=978-3-319-23042-9
LaTeX in 24 Hours
Dilip Datta
http://link.springer.com/openurl?genre=book&isbn=978-3-319-47831-9
Introduction to Statistics and Data Analysis
Christian Heumann, Michael Schomaker, Shalabh
http://link.springer.com/openurl?genre=book&isbn=978-3-319-46162-5
Principles of Data Mining
Max Bramer
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-7307-6
Computer Vision
Richard Szeliski
http://link.springer.com/openurl?genre=book&isbn=978-1-84882-935-0
Data Mining
Charu C. Aggarwal
http://link.springer.com/openurl?genre=book&isbn=978-3-319-14142-8
Computational Geometry
Mark de Berg, Otfried Cheong, Marc van Kreveld, Mark Overmars
http://link.springer.com/openurl?genre=book&isbn=978-3-540-77974-2
Robotics, Vision and Control
Peter Corke
http://link.springer.com/openurl?genre=book&isbn=978-3-319-54413-7
Statistical Analysis and Data Display
Richard M. Heiberger, Burt Holland
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2122-5
Statistics and Data Analysis for Financial Engineering
David Ruppert, David S. Matteson
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2614-5
Stochastic Processes and Calculus
Uwe Hassler
http://link.springer.com/openurl?genre=book&isbn=978-3-319-23428-1
Statistical Analysis of Clinical Data on a Pocket Calculator
Ton J. Cleophas, Aeilko H. Zwinderman
http://link.springer.com/openurl?genre=book&isbn=978-94-007-1211-9
Clinical Data Analysis on a Pocket Calculator
Ton J. Cleophas, Aeilko H. Zwinderman
http://link.springer.com/openurl?genre=book&isbn=978-3-319-27104-0
The Data Science Design Manual
Steven S. Skiena
http://link.springer.com/openurl?genre=book&isbn=978-3-319-55444-0
An Introduction to Machine Learning
Miroslav Kubat
http://link.springer.com/openurl?genre=book&isbn=978-3-319-63913-0
Guide to Discrete Mathematics
Gerard O’Regan
http://link.springer.com/openurl?genre=book&isbn=978-3-319-44561-8
Introduction to Time Series and Forecasting
Peter J. Brockwell, Richard A. Davis
http://link.springer.com/openurl?genre=book&isbn=978-3-319-29854-2
Multivariate Calculus and Geometry
Seán Dineen
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-6419-7
Statistics and Analysis of Scientific Data
Massimiliano Bonamente
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-6572-4
Modelling Computing Systems
Faron Moller, Georg Struth
http://link.springer.com/openurl?genre=book&isbn=978-1-84800-322-4
Search Methodologies
Edmund K. Burke, Graham Kendall
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6940-7
Linear Algebra Done Right
Sheldon Axler
http://link.springer.com/openurl?genre=book&isbn=978-3-319-11080-6
Linear Algebra
Jörg Liesen, Volker Mehrmann
http://link.springer.com/openurl?genre=book&isbn=978-3-319-24346-7
Algebra
Serge Lang
http://link.springer.com/openurl?genre=book&isbn=978-1-4613-0041-0
Understanding Analysis
Stephen Abbott
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2712-8
Linear Programming
Robert J Vanderbei
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-7630-6
Understanding Statistics Using R
Randall Schumacker, Sara Tomek
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6227-9
An Introduction to Statistical Learning
Gareth James, Daniela Witten, Trevor Hastie, Robert Tibshirani
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-7138-7
Statistical Learning from a Regression Perspective
Richard A. Berk
http://link.springer.com/openurl?genre=book&isbn=978-3-319-44048-4
Applied Partial Differential Equations
J. David Logan
http://link.springer.com/openurl?genre=book&isbn=978-3-319-12493-3
Robotics
Bruno Siciliano, Lorenzo Sciavicco, Luigi Villani, Giuseppe Oriolo
http://link.springer.com/openurl?genre=book&isbn=978-1-84628-642-1
Regression Modeling Strategies
Frank E. Harrell , Jr.
http://link.springer.com/openurl?genre=book&isbn=978-3-319-19425-7
A Modern Introduction to Probability and Statistics
F.M. Dekking, C. Kraaikamp, H.P. Lopuhaä, L.E. Meester
http://link.springer.com/openurl?genre=book&isbn=978-1-84628-168-6
The Python Workbook
Ben Stephenson
http://link.springer.com/openurl?genre=book&isbn=978-3-319-14240-1
Machine Learning in Medicine — a Complete Overview
Ton J. Cleophas, Aeilko H. Zwinderman
http://link.springer.com/openurl?genre=book&isbn=978-3-319-15195-3
Object-Oriented Analysis, Design and Implementation
Brahma Dathan, Sarnath Ramnath
http://link.springer.com/openurl?genre=book&isbn=978-3-319-24280-4
Introduction to Data Science
Laura Igual, Santi Seguí
http://link.springer.com/openurl?genre=book&isbn=978-3-319-50017-1
Applied Predictive Modeling
Max Kuhn, Kjell Johnson
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6849-3
Python For ArcGIS
Laura Tateosian
http://link.springer.com/openurl?genre=book&isbn=978-3-319-18398-5
Concise Guide to Databases
Peter Lake, Paul Crowther
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-5601-7
Digital Image Processing
Wilhelm Burger, Mark J. Burge
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-6684-9
Bayesian Essentials with R
Jean-Michel Marin, Christian P. Robert
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-8687-9
Robotics, Vision and Control
Peter Corke
http://link.springer.com/openurl?genre=book&isbn=978-3-642-20144-8
Foundations of Programming Languages
Kent D. Lee
http://link.springer.com/openurl?genre=book&isbn=978-3-319-70790-7
Introduction to Artificial Intelligence
Wolfgang Ertel
http://link.springer.com/openurl?genre=book&isbn=978-3-319-58487-4
Introduction to Deep Learning
Sandro Skansi
http://link.springer.com/openurl?genre=book&isbn=978-3-319-73004-2
Linear Algebra and Analytic Geometry for Physical Sciences
Giovanni Landi, Alessandro Zampini
http://link.springer.com/openurl?genre=book&isbn=978-3-319-78361-1
Applied Linear Algebra
Peter J. Olver, Chehrzad Shakiban
http://link.springer.com/openurl?genre=book&isbn=978-3-319-91041-3
Neural Networks and Deep Learning
Charu C. Aggarwal
http://link.springer.com/openurl?genre=book&isbn=978-3-319-94463-0
Data Science and Predictive Analytics
Ivo D. Dinov
http://link.springer.com/openurl?genre=book&isbn=978-3-319-72347-1
Analysis for Computer Scientists
Michael Oberguggenberger, Alexander Ostermann
http://link.springer.com/openurl?genre=book&isbn=978-3-319-91155-7
Excel Data Analysis
Hector Guerrero
http://link.springer.com/openurl?genre=book&isbn=978-3-030-01279-3
A Beginners Guide to Python 3 Programming
John Hunt
http://link.springer.com/openurl?genre=book&isbn=978-3-030-20290-3
Advanced Guide to Python 3 Programming
John Hunt
http://link.springer.com/openurl?genre=book&isbn=978-3-030-25943-3