macOS Sierra ALL features page In previous releases Apple had an "All Features" or "New Enhancements" page buried somewhere off the main Mac OS X page. It listed features that were beyond just the main marketing ones. Does anybody know where this information lives for Sierra?

10.6: http://web.archive.org/web/20110328202042/https://www.apple.com/macosx/refinements/enhancements-refinements.html

10.7:
http://web.archive.org/web/20120329193957/http://www.apple.com/macosx/whats-new/features.html

10.8:
http://web.archive.org/web/20130405191728/http://www.apple.com/osx/whats-new/features.html

10.9:
http://web.archive.org/web/20140729182042/http://www.apple.com/osx/whats-new/features.html

10.10:
http://web.archive.org/web/20150912081700/https://www.apple.com/osx/all-features/

10.11:
http://web.archive.org/web/20160710162027/http://www.apple.com/osx/all-features/
I wasn't able to find full, straight-from-the-Apple's-mouth release notes for Sierra, but you can find developer-level release notes for all versions of macOS since OS X 10.6 on this page on the Apple developer website. The notes for macOS Sierra 10.12 can be found here and those for 10.12.1 can be found here. However, note the caveat:

This document describes key developer-level features that were introduced in different versions of macOS.
This document is not intended as a complete list of features or changes for each new version of macOS. Instead, it focuses on those features or changes that affect the development of third-party software, providing overviews of each along with insight into how and when you might use them to create your own software.