diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index 90d511a79..1f8d3a00e 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -102,7 +102,7 @@ Books on general-purpose programming that don't focus on a specific language are
     * [Ember.js](#emberjs)
     * [Express.js](#expressjs)
     * [Fastify](#fastify)
-    * [Hydrogen](#hydrogen)  
+    * [Hydrogen](#hydrogen)
     * [Ionic](#ionic)
     * [jQuery](#jquery)
     * [meteor](#meteor)
@@ -352,7 +352,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Easy 6502](http://skilldrick.github.io/easy6502/) - Nick Morgan
 * [Machine Language for Beginners](https://archive.org/details/ataribooks-machine-language-for-beginners) - Richard Mansfield
 * [MIPS Assembly Language Programming Using QtSpim](http://www.egr.unlv.edu/~ed/MIPStextSMv11.pdf) - Ed Jorgensen (PDF)
-* [Programmed Introduction to MIPS Assembly Language](http://chortle.ccsu.edu/AssemblyTutorial/index.html) 
+* [Programmed Introduction to MIPS Assembly Language](http://chortle.ccsu.edu/AssemblyTutorial/index.html)
 * [The Second Book of Machine Language](http://www.atariarchives.org/2bml/)
 
 
@@ -602,7 +602,7 @@ Books on general-purpose programming that don't focus on a specific language are
 ### CoffeeScript
 
 * [CoffeeScript Cookbook](https://coffeescript-cookbook.github.io)
-* [CoffeeScript Ristretto](https://leanpub.com/coffeescript-ristretto/read) - Reginald Braithwaite 
+* [CoffeeScript Ristretto](https://leanpub.com/coffeescript-ristretto/read) - Reginald Braithwaite
 * [Hard Rock CoffeeScript](https://alchaplinsky.github.io/hard-rock-coffeescript/) - Alex Chaplinsky (gitbook)
 * [Smooth CoffeeScript](http://autotelicum.github.io/Smooth-CoffeeScript/SmoothCoffeeScript.html)
 * [The Little Book on CoffeeScript](http://arcturo.github.io/library/coffeescript/) - Alex MacCaw, David Griffiths, Satoshi Murakami, Jeremy Ashkenas
@@ -2005,7 +2005,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Python 2 Official Documentation](https://docs.python.org/2/download.html) (PDF, HTML, TEXT) (2.x)
 * [Python 2.7 quick reference](https://web.archive.org/web/20171013204449/http://infohost.nmt.edu/tcc/help/pubs/python27/python27.pdf) - John W. Shipman (PDF) (2.7) *(:card_file_box: archived)*
 * [Python 3 Official Documentation](https://docs.python.org/3/download.html) (PDF, EPUB, HTML, TEXT) (3.x)
-* [Python 3 Patterns, Recipes, and Idioms](https://python-3-patterns-idioms-test.readthedocs.io/en/latest/) - Bruce Eckel & Friends 
+* [Python 3 Patterns, Recipes, and Idioms](https://python-3-patterns-idioms-test.readthedocs.io/en/latest/) - Bruce Eckel & Friends
 * [Python 3 Tutorial](https://github.com/Akuli/python-tutorial)
 * [Python Data Science Handbook](https://jakevdp.github.io/PythonDataScienceHandbook) - Jake VanderPlas (HTML, Jupyter Notebooks)
 * [Python for Astronomers](https://prappleizer.github.io/textbook.pdf) - Imad Pasha, Christopher Agostino (PDF)
@@ -2158,7 +2158,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [R Packages](https://r-pkgs.org) - Hadley Wickham, Jenny Bryan
 * [R Practicals](http://www.columbia.edu/~cjd11/charles_dimaggio/DIRE/resources/R/practicalsBookNoAns.pdf) (PDF)
 * [R Programming](https://en.wikibooks.org/wiki/R_Programming) - Wikibooks
-* [R Programming for Data Science](https://bookdown.org/rdpeng/rprogdatascience/) - Roger D. Peng 
+* [R Programming for Data Science](https://bookdown.org/rdpeng/rprogdatascience/) - Roger D. Peng
 * [R Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/rsuccinctly) (PDF, Kindle) (email address *requested*, not required)
 * [Statistical Inference via Data Science](https://moderndive.com) - Chester Ismay, Albert Y. Kim
 * [Summary and Analysis of Extension Program Evaluation in R](https://rcompanion.org/handbook/index.html) - Salvatore S. Mangiafico
diff --git a/more/free-programming-interactive-tutorials-en.md b/more/free-programming-interactive-tutorials-en.md
index 3fe4db41e..545d88759 100644
--- a/more/free-programming-interactive-tutorials-en.md
+++ b/more/free-programming-interactive-tutorials-en.md
@@ -403,6 +403,7 @@
 
 ### Ruby
 
+* [A Brief Introduction to Ruby](https://markm208.github.io/rubybook) - Mark Mahoney
 * [CodeCademy Ruby](https://www.codecademy.com/learn/ruby)
 * [Ruby Koans](http://www.rubykoans.com)
 * [The Odin Project](http://www.theodinproject.com)