As you know GITHUB is one of the most popular brand in programming world. It is one of the largest code hosted platform having more than 31 million repositories and all are open source. Code Review is one of the essential Part of GITHUB Workflow like this way – Pull Request = Code + Issue + Code Comments
You can easily manage all the teams within organizations. Members can be granted READ, R/W or Admin Level privileges to repositories. Whenever you create a new team or mention a team within thread, all team members will receive a notification.
Now GitHub announced the biggest free learning material in his platform and the original contributor of this stuff is Mr. George Stocker
They published more than 100+ Topics including Programming Languages E-books, Materials, OS related materials, Database related stuff, Software stuff, podcasts, video tutorials, Screen casts, problem solving stuff etc..
Here you can find all the free learning stuff/Material/Tutorials/E-books/Guides/Whitepapers/Research Papers etc..
They also published all the stuff in other languages too, for that you can click here