Nexus Guide (Scrum.org)
What: The Nexus guide is the 10 page description of a way to work with multiple teams in a scaled environment. It was created in 2015 by Ken Schwaber and is heavily reliant on the original Scrumguides. So, before reading Nexus, make sure you are well up to speed with Scrum.
Why: It is a light weight, free and even without completely using this approach, it may provide some nice focus areas and insights to start improving or creating your own scaling setup
Who: It has been developed by Scrum-founding-father Ken Schwaber and is provided by Scrum.org.
Direct download: English version Nexus Guide 1.1.