Apple has announced that iOS 11 will be released to the general public on September 19 as a free download.
Additionally, macOS High Sierra will debut as a free download on September 25 for Mac users.
iOS 11 Release Date: September 19
The September 19 release date for iOS 11 was announced during the iPhone X and iPhone 8 event, and also appears on the iOS 11 page at Apple.com.
iOS 11 is compatible with many modern iPhone, iPad, and iPod touch, you can see the full iOS 11 compatible devices list here.
In addition to iOS 11, September 19 will also be the launch date of watchOS 4 and tvOS 11 for Apple Watch and Apple TV.
Always backup an iOS device before installing system software updates.
MacOS High Sierra Release Date: September 25
MacOS High Sierra was not mentioned during the Apple event, however Apple updated their Mac webpage with a small mention of the release date being set for September 25.
A list of Macs which support MacOS High Sierra 10.13 can be found here.
Be sure to back up a Mac before attempting to install macOS High Sierra or any other system software update.
Users who are currently enrolled in the public beta and developer beta testing programs will be able to update directly to the final versions of iOS 11 and macOS High Sierra when they are available.
Currently, iOS 11 GM is available to download along with GM builds of watchOS 4 and tvOS 11. A GM build of macOS High Sierra is likely to arrive soon as well.