Those with Macs, iPhones, or both in their lives will find software updates waiting for them today. Apple has released version 10.11 of OS X, code-named El Capitan, to the public today along with a minor iOS update, version 9.0.2.
OS X El Capitan doesn't fundamentally alter the Mac experience much—it's an improvements and refinements kind of release. A new system font, called San Francisco, is probably the most visible change over OS X Yosemite. GPU-intensive animations like Mission Control and smooth scrolling are much, much more buttery on my MacBook Pro's Intel IGP than they were on Yosemite, probably thanks to the arrival of the Metal low-level graphics API. Apple rewrote key system components like Core Animation and Core Graphics to take advantage of this API, and the results really are tangible. The API change is supposed to improve gaming performance on OS X, too.
OS X El Capitan is a free upgrade from the Mac App Store, and the process was smooth on my Mac, so it's probably worth downloading and installing if you have a compatible machine. For more information, check out Apple's list of changes, or avail yourself of Ars Technica's famous book-length review for all of the details.
iOS 9.0.2 doesn't bring nearly as many changes as Yosemite. Most notably, Apple corrected a lock screen bug that let attackers with physical access to the device get into the owner's photos and contacts. The update also includes some minor bug fixes and stability improvements. Users can find the update in the Settings app's General section under Software Update.