An illustrated introduction to Bayesian statistics using Jupyter notebooks. I was always confused about the difference between Bayesian and Frequentist approaches until I read this.

An online book focusing on the fundamentals of data science (statistics, traditional machine learning). I don't know much about R (on which this book is based) but most of the theory in there is relevant for any junior data scientist.

Brief introductory book to essential statistics. This online book is very clear and helped me understand concepts I always found confusing.