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