Apple Pay is also coming to the Mac via the web. "So now when you're shopping online, you'll have a pay with Apple Pay button," Apple's senior vice president of Software Engineering Craig Federighi said. Authentication is made with your iPhone's Touch ID fingerprint sensor.

For sites and online stores that support Apple's payment service, anyone will be able to tap the "Pay with Apple Pay" button and have a notification pop up on their phone.

Auto Unlock

Auto-unlock is one new feature that lets you automatically unlock your Mac when it detects you're wearing your Apple Watch right near it.

 It can tell when you’re nearby - by detecting your Apple Watch or iPhone - and then simply unlocks your Mac, and doesn't ask for your password. What's more, it can tell that it's you and won't just unlock with anyone's iPhone or Apple Watch nearby, so it's secure.

Universal Clipboard

Universal clipboard is another new continuity feature, which lets you easily and quickly copy and paste information between iOS and Mac devices near each other. What that means in simple terms is that if you copy an image, or a selection of text or a video on your iPhone, you'll be able to paste that on to a document or email from your Mac. Or vice versa.

Desktop and Documents on all devices

iCloud Drive will now let you get access to the files on your desktop from any other Mac, or even from your iPhone or iPad. Any files you have saved on your desktop on a Mac, or within the Documents folder, will automatically show up in iCloud Drive. On an iPhone or iPad you can get access to them by using the iCloud Drive app, and if you have a PC you can use iCloud.com or the iCloud for Windows app. What's more, if you have a second Mac, the files automatically become available on the desktop and in the Documents folder.

Messages app overhaul

Like iOS 10, the Messages app for macOS Sierra is getting a feature overhaul bringing web link previews and in-app video watching, reactions, and bigger, better emoji.

Optimised Storage

Optimised storage lets you automatically move stuff from your Mac into the cloud, or even deletes stuff you don’t need. With all the automatic options switched on, Apple uses the example of increasing 20GB available storage to up to 150GB.

It essentially works by moving anything you don't use often in to iCloud, reminding you to delete things like used app installers or disk images, and clears out duplicate downloads, logs and caches. It basically removes stuff you didn't even know was there, which is more than likely taking up space you could be using for something else. In the past, this has been achieved by downloading third party apps like CleanMyMac, but it's now being built right in to the operating system.

Tabs

Part of macOS Sierra is a new Tabs API which lets software engineers add tabs to any apps, without much work from those developers. Like Finder and Safari, creating tabs will be simple for the user too. Any app that supports multiple windows will get support for tabs, meaning you can - for instance - have Maps open in multiple locations at once, or you can switch between more than one Mail email draft, or even copy and paste text between different Pages documents without needing more than one window open on screen.

Picture in Picture

With Picture in Picture, you’ll be able to have a small video window play while you continue with your main functions. Videos in Safari and iTunes will have a new pop-out icon. Click on it, and the video leaves the web page and takes up its own small window on screen. You'll also be able to resize this window, just like you can on the iPad. What's more, it follows you when you switch between desktop spaces, so you never lose sight of what you're watching.

Photos app memories

Apple has built a lot of smarts in to its Mac Photos app. Similar to Google Photos, it can create curated collections of important occasions without you having to do anything. It's also been trained to recognize people, places and objects and groups them accordingly.

macOS Sierra: Release date

macOS Sierra is available as developer preview now, and a public beta being launched a little later this summer, in July. For those who don’t want to play with a non-finished version, the update will be ready for consumers by around October/November time.