Springer just released 408 books for free that you could download and enjoy. For those with computer skills, there is a python script that allow you to download them all at the same time.
https://www.reddit.com/r/FreeEBOOKS/comments/g34xi5
https://www.reddit.com/r/FreeEBOOKS/comments/g34xi5
Likes:
Pooya and Zob Ahan