Now that El Capitan OS X 10.11 is out, here are some excellent resources available to help you in researching what is new, learning how to take advantage of the software and work through any issues you might encounter.
El Capitan: TidBITS Answers Your Questions
El Capitan: The MacStories Review by Alex Guyot
El Capitan: The Ars Technica Review by Andrew Cunningham & Lee Hutchinson
Complete OS X El Capitan review by Rene Ritchie
Apple’s OS X page
System Integrity Protection (a.k.a. rootless) deep dive by Rich Trouton …