The Open Source community is amazing, they do great work and share it freely with the world. I have compiled a list of free books and will continue to update it as I find more.
- R for Data Science
- Efficient R programming
- Creating Websites with R Markdown
- R Markdown: The Definitive Guide
- Text Mining with R
- Happy Git and GitHub for the useR
- Modern Data Science with R
- The Unix Workbench
- Data Visualization - A practical introduction
- The Art of Data Science
- Interactive web-based data visualization with R, plotly, and shiny
- STAT 545
- R Programming for Data Science
- Geocomputation with R
- Statistical Inference via Data Science
- Forecasting: Principles and Practice
- Data Science Live Book
- Agile Data Science with R
- Mastering Shiny
- Introduction to R
- Data Wrangling with R
- Data Visualization with ggplot2
- Data Visualization with R
- R, Databases & SQL
- Advanced R
A great source for finding books: - Here