Apple published security updates and bulletins for six products such as Xcode 9, tvOS 11, watchOS 4, Safari 11, iOS 11, and iTunes 12.7 (for both macOS and Windows).
The security updates were published to address several low-level security issues. The most important of all the security patches is the one delivered with the recently launched iOS 11. For an overview of all the new (non-security related) features in iOS 11, you can read this review from MacRumors.
There are no macOS security updates. Apple will release macOS High Sierra (10.13) on September 25, and the company is expected to bundle any security patches with the main 10.13 release.