iOS 10, watchOS 3, and tvOS 10 released

Today Apple released updates for nearly all of their non-Mac devices: iPhone, iPad, iPod Touch, Apple Watch, and Apple TV. Lots of new new features!WARNING - These initial "point oh" releases, while perfectly fine for the vast majority of users, occasionally cause serious problems for a very small group of people. If you don't want to risk being in this (possible) minority wait three or four days, by which point Apple will have likely fixed any of these bugs which may or may not exist. Before you upgrade be sure that you have a backup and that you have a few hours available to fix it in case something does go wrong. Which are probably good precautions to take in any upgrade, but particularly important if you're gonna jump on these big updates immediately.

Updates include:

iOS - note that this is labeled as 10.0.1. To upgrade go to Settings > General > Software Update.

New lock screen experience (read this article that explains the changes)
Deeper support for 3D touch
Most built-in apps are removable
Mail conversation view
More immersive iMessage experience
Siri works with supported third party apps "Get me an Uber to Dulles" or "PayPal John 20 dollars"
Third party integration for Maps, such as Uber and OpenTable
Much deeper HomeKit support
Redesigned Music app
Rich notifications
ApplePay in Safari
Multilingual typing, no need to manually switch languages

watchOS - to upgrade first upgrade your iPhone, then on your paired iPhone go to the Watch app > General > Software Update.

Holy frak it's fast!
Reminders app
HomeKit app
Minnie Mouse watch face
Quick switching between watch faces
Manipulate watch faces and complications from the Apple Watch app on your iPhone

tvOS - to upgrade go to Settings > System > Software Update.

Siri search by topic
HomeKit commands using Siri
Single Sign On allows you to log in once for your TV provider for all apps
Dark Mode option
Option to auto-install apps you purchase on your iPhone or iPad