Springer Nature offer free access to 500 essential textbooks(springernature.com)

   Introduction to Evolutionary Computing
   Data Structures and Algorithms with Python
   LaTeX in 24 Hours
   Automata and Computability
   The Algorithm Design Manual
   Principles of Data Mining
   Fundamentals of Business Process Management
   UML @ Classroom
   Foundations for Designing User-Centered Systems
   Computer Vision
   Data Mining
   Computational Geometry
   Cryptography Made Simple
   Eye Tracking Methodology
   The Data Science Design Manual
   An Introduction to Machine Learning
   Guide to Discrete Mathematics
   Modelling Computing Systems
   Understanding Cryptography
   Concise Guide to Software Engineering
   Fundamentals of Multimedia
   The Python Workbook
   Recommender Systems
   Python Programming Fundamentals
   Object-Oriented Analysis, Design and Implementation
   Introduction to Data Science
   Concise Guide to Databases
   Digital Image Processing
   Guide to Computer Network Security
   Foundations of Programming Languages
   Probability and Statistics for Computer Science
   Guide to Competitive Programming
   Introduction to Artificial Intelligence
   Introduction to Deep Learning
   A Beginner's Guide to Scala, Object Orientation and Functional Programming
   Fundamentals of Business Process Management
   Guide to Scientific Computing in C++
   Fundamentals of Java Programming
   Logical Foundations of Cyber-Physical Systems
   Introduction to Programming with Fortran
   Neural Networks and Deep Learning
   Data Science and Predictive Analytics
   Systems Programming in Unix/Linux
   Introduction to Parallel Computing
   Analysis for Computer Scientists
   Introductory Computer Forensics
   Java in Two Semesters
   A Beginners Guide to Python 3 Programming
   Advanced Guide to Python 3 Programming