Apple unveiled iOS 10 at the World Wide Developers Conference on June 13, 2016. 7 public betas and several developer betas were released after June. Apple released the final “Gold Master" version for developers on September 7, and announced that the final public version will be available on September 13, 2016.
iOS 10 includes a variety of new features and upgrades, including new messaging features, new emojis, the ability to delete stock apps an more. You can download the public version on September 13 by navigating to Settings > General > Software Update on your supported device. You can see a complete list of iOS 10 supported devices here.