Files on desktop now sync to iCloud.
That means desktop files will appear on all devices you're logged into, including Macs, iPhones, and iPads.
See? That photo of LeBron I saved to the desktop immediately appeared on the iCloud Drive iPhone app.
The Photos app can scan your library and help you find photos easier using image recognition.
For example, search "cat" and get all your cat photos.
The app will also group photos into albums automatically based on location and the people in them. Click on the Memories tab to view.
Apple does all its image recognition on your device and doesn't store your data on its servers. It's very similar to how Google Photos works on the web.
It'll remove files like iTunes videos and other large items and store them in iCloud. You can download them again later.
Apple says this will save several gigabytes of space for many users.
You can play videos in a picture-in-picture window on your desktop. It works with web videos and iTunes. Click the the special icon on the video player...
You can resize and move the video around too.
This feature only works with web videos you watch in Safari. You can't use it with Chrome or Firefox. So far, only a few web video services have enabled picture-in-picture, but there's nothing stopping more from adding it now that Sierra is available.
You can run multiple tabs in many apps, just like you can in a web browser.
Apple says most app developers won't have to change their code to use this feature. It'll happen automatically in Sierra.
iMessage on Mac is getting a lot of new features, just like it is in iOS 10. For example, emojis are three times larger. You can also react to messages with stickers.
Just don't go too crazy with stickers!
It has big, bold fonts and art.
The rest of iTunes pretty much looks the same as before, unfortunately. iTunes is long overdue for a redesign.
The notifications window has a new look. Widgets now appear in the Today tab, and you can customize them as you see fit.
But this is the biggest change: Siri is now on the Mac. You can do a lot with it, like search for images.
You open Siri from the icon in the dock or the taskbar.
Siri is a quick way to search for files on your computer.
Here's the result when you ask for audio files, but you can search for documents, photos, and everything else.
And tell you the weather.
That's not all, of course. Searches are pretty much the same as they are on the iPhone.
But sending messages or emails with your voice isn't much easier than just typing them the old-fashioned way.
What else?
On top of everything you just saw, you'll also be able to use Apple Pay to shop in Safari (if the retailer supports it), unlock your Mac without a password if you're wearing your Apple Watch, and copy/paste items between your iPhone and Mac.
So is Sierra any good?
Sierra is a nice update, but it won't fundamentally change how you use your Mac. Siri is an interesting addition, but sometimes it can be a bit awkward talking to your computer, especially while you're at work or in a public setting.
Sierra has loads of tiny improvements, but they add up to a worthy upgrade. Plus, it's free, so what do you have to lose?