In iOS 10, developers will be able to tie their apps into Siri, Messages, Maps, and Phone — and that means we'll spend less time launching their apps.
In iOS 10, Apple seems to be taking a slightly different approach to extensibility. It is now centered around the company's stock apps, making it unnecessary — in many cases — for you to ever leave Messages, Maps, Safari, and Siri for other, third-party apps and services. Built-in apps are all about app extensions and here are a few of our favorites.

Siri + Apps

Siri on iOS 10
When iOS 10 launches in the fall, you'll likely see many apps touting support for Siri. From ride booking and payments to workouts and messaging, you'll be able to control several categories of apps using Siri.
But here's the thing: Siri interactions are shown within the Siri interface — not within individual apps and services. You'll ask Siri to get you a ride to your hotel via Lyft, for example, and a card will show you all the necessary information.
Let's just think about that:
  1. Trigger Siri via "Hey, Siri" or a long press on the Home button.
  2. Issue a command or make a request.
  3. Tap a couple times to make the necessary adjustments and confirm.
That's it. And you didn't even have to launch an app.

iMessage + Apps

iMessage apps on iOS 10
Apple's said time and time again Messages is the most used app on iOS. It makes sense — it's where most people have the majority of their interactions. And in iOS 10, Apple's going to make sure even more interactions happen there.
Developers will be able to create iMessage Apps that let you share content, send money, edit photos, and even play games. All without — say it with me — launching a third-party app.
I love the idea of being able to open up Messages, start a group message, set up a get-together with friends, and split the cost all without leaving the app.

Maps + Apps

Maps apps on iOS 10
In iOS 10, location-related apps (think ride booking, hotel and restaurant reservations, etc.) will be able to tie-in with Apple's Maps app.
Say you're browsing the map of a new area and come across a restaurant that sounds interesting; you can use a restaurant reservation app right within Maps to secure your table.
I don't often use Maps, but man-oh-man it'd be nice to do all my travel planning right within Apple Maps, y'know, without ever having to launch any third-party apps.
Are you seeing it yet?

Phone + Apps

Phone apps on iOS 10
Why worry about launching WhatsApp or Slack or Skype to make or take a VoIP call? In iOS 10, developers will be able to integrate their VoIP services with the Phone app.
If Uncle Andrew always calls you over Skype, you can get a Phone-style fullscreen notification on the lock screen and access all the features and functions of a Skype call without having to head to the app.

Don't touch that app tile!

I don't know about you, but Apple's extensibility improvements in iOS 10 seem like a real "I see what you did there" moment. It is, in most cases, a better user experience if people don't have to jump between apps dozens of times to get work done (see: Split View).
In iOS 10, Apple's making third-party apps come to you, so it's not the other way around. There'll be less Spotlight searching for that one app that's buried in your "Misc." folder, scrolling through six Homes screen pages to find your ride-hailing app, or scanning line-after-line of apps to find your favorite calculator app.
I, for one, welcome our iOS stock app overlords.