Following on from the Technical Preview of Windows 10 last year, Microsoft has unveiled a host of new features in Windows 10 and shown how it will work on all kinds of devices, including smartphones, tablets and even the Xbox One.
Windows 10: a free upgrade
Before we delve into that, though, there's one other important detail: price. For the first year, Windows 10 will be a free upgrade for anyone running Windows 8 (or 8.1) and you can even upgrade for nothing if your PC has Windows 7.
Similarly, anyone with a smartphone running Windows Phone 8 (or 8.1) will be able to update to Windows 10 - not Windows Phone 10, note - for free.
This is a win-win situation, since we'll all be able to benefit from the new features without opening our wallets and Microsoft will quickly gain a large user base to woo developers into creating apps for Windows 10.
Windows 10: one platform, multiple devices
Critical to Windows 10's success is the fact that it will run on PCs, laptops, tablets, smartphones and the Xbox one. With a few exceptions, it means the same apps will be available on all Windows 10 devices. For example, smartphones running Windows 10 will have built-in Office and Outlook.
Obviously, the interface will be tailored so it works on the vastly different screen sizes but as Microsoft demonstrated at the launch event in Redmond on January 21st, it's the same underlying code running on smartphones and PCs.
Microsoft calls these Universal apps, and they'll sync with each other so changes you make on one device are reflected on another.
Universal apps will work with phones, small tablets and PCs, delivering everything you need for productivity. A family of apps will be built into all Windows 10 devices, bringing continuity as you move from device to device. Full Word, Excel and PowerPoint will be included on phones - complete with the familiar Office Ribbon. A recent documents list will be available to all Windows 10 devices.
Many apps will get a big overhaul for Windows 10, not just Office and Outlook. The Photos app has been improved so you'll see the same photo stream across your Windows 10 devices. And like Google Auto Awesome, photos will be automatically enhanced (if you allow it) and duplicates removed with the best version of similar photos kept.
Windows 10: Action Center and settings
Windows Phone's Action Center will be coming to desktop in Windows 10. It will offer notifications, quick actions and more, similar to the Notification Center in OS X Yosemite for Mac users.
Settings have also been streamlined and implemented as a universal app, removing the confusion of having both a Control Panel and Settings menu.
Windows 10: Cortana
One of the most anticipated new features was Cortana, which will come to the PC and tablet for the first time with Windows 10 thanks to the new way that Microsoft has merged the operating system for mobile and desktop into one.
Microsoft has pipped Apple to the post here, bringing system-wide voice control to the PC. You can also type to interact with Cortana if you prefer. (Below, left, is Cortana on a smartphone running Windows 10.)
One of the big benefits of having Cortana on all your devices is 'her' knowledge of you and your interests. For example, you could ask Cortana to send an email to your wife and then dictate it without leaving the application you're using. Cortana knows who you're related to (if you tell her) so she can send the email without asking for further details.
Similarly, with access to your emails and calendars, Cortana can be aware of important events and let you know if you need to leave early due to heavy traffic, for example.
Windows 10: Project Spartan
A new web browser will ship with Windows 10, currently code-named Project Spartan. Spartan has a new rendering engine that's "compatible with today's web". It has a new look and feel, and it has three significant features that will make you more productive on the web, according to Microsoft.
First is the ability to mark up articles on the web with comments and annotations before you share them, either through touch or with a keyboard. Second, Spartan improves reading on the web.
Second is that its reading mode supports PDFs natively and can be personalised, and includes a reading list that shows up on all your Windows 10 devices. This content is then available to read offline, so it won't matter if you're on a plane with no internet connection.
Third, Spartan brings Cortana to the browser and will pop up information and suggestions as you browse the web. When you search, Cortana can display information (similar to Google's widgets) at the top. If you search for flight status and Cortana knows a particular flight number from an email or your calendar, she can show whether the flight is on time or delayed.
Windows 10: Xbox
Microsoft got Xbox all wrong in Windows 8. Instead of an app for Xbox owners who also have a Windows PC, the Xbox apps in Windows 8 were almost adverts to persuade people who didn't already have one to go and buy the console. The music, videos and games apps in Windows 8 made the mistake of putting paid-for store content before your own stuff, but that won't happen in Windows 10.
Thankfully, Microsoft is bringing Xbox Live to the desktop. Players will also be able to play Xbox One games on their PC by streaming them directly from their console to their Windows 10 tablet or PC within their home. That means you don't need a powerful device to play Xbox One games, and it's handy if someone else wants to watch the TV your console is connected to.
Better still, Windows 10 gamers will be able to play against people on their Xbox One in multiplayer games: it's the same platform, remember.
Game recording will also be built into Windows 10 for Windows games. This means you'll be able to use a shortcut (Win-G) to open the Game DVR interface and do things such as saving the last 30 seconds of gameplay and share it with people or post it to Facebook, YouTube and other places.
Windows 10: Continuum
One of the hurdles for the design team is hybrid, or 2-in-1 devices which can be a tablet or a laptop. In laptop mode, you need an interface which is optimised for keyboard and mouse, but as a tablet you want to control everything via the touchscreen.
Microsoft's answer is Continuum, which automatically switches modes when you disconnect the keyboard from a Surface tablet. (If the keyboard is part of the device, we're assuming there will be a button or a way to detect when you fold the keyboard underneath the screen to use it as a tablet.)
For example, if you have several windows open which don't fill the entire screen, they'll automatically switch to full-screen mode and possibly even change to a touch-friendly UI when you go to tablet mode.
Windows 10: Smartphones and tablets
For devices with 8in screens or smaller there will be a 'mobile' version of Windows 10. On a smartphone, the Start screen is very similar to Windows Phone 8 with live tiles and the ability to rearrange and resize tiles as you like.
When you swipe in from the right you'll see the app tray (just as you do now) but you'll find recently installed apps at the top of the list.
The Action Centre also has some new features and is now synched with the PC version. You can expand action buttons and dismiss single items shown as notifications.
The Word Flow keyboard has been improved in Windows 10, letting you pull it over to the right and doing shape writing with one hand, and you can use voice input to reply to messages by tapping the microphone button. The speech system is sophisticated enough to recognise names of contacts, hashtags and insert punctuation.
Other improvements to messaging include support for IP-based messaging services and Skype. If you're sending an SMS and both parties use Skype, Windows 10 will automatically flip to Skype so you can have a real-time conversation, whether that's continuing to use IM, or switching to a voice or video call.
As we've already said, smartphones will have Office built-in and thanks to hardware acceleration you'll be able to give proper presentations from your phone:
New versions of Outlook Mail and Outlook Calendar will also be found on phones, tablets and PCs. The full Word engine will be built into the email app so you can format text just as you would in a document. Swipe gestures - as already exist in Apple Mail and Gmail - let you flag or delete messages.
Windows 10: HoloLens
A surprise announcement was that Microsoft is working on an augmented reality system called HoloLens. It's part of Windows 10 and involves a headset a little like Google Glass.
It goes beyond augmented reality - we're told - because HoloLens lets you interact with the 'holograms' you see. Calling the graphics holograms is a bit misleading, but the idea is that you can have content wherever you want. From watch a movie or TV show on a virtual screen to 'pinning' a shopping list to the fridge, or even playing games - such as Minecraft here - in a virtual 3D environment.
You're not cut off from the real world since the wireless glasses are transparent. It's certainly an interesting concept with a lot of potential, and we're eager to see how it develops.
Windows 10: When's it available?
The great thing is that Microsoft wants as many people as possible to help shape Windows 10. This means you can sign up to the Windows Insider Program and download the preview version of Windows 10 to test out, all for free. Note that the latest build with the consumer features we've talked about above won't be available until next week, though.
Simply head to preview.windows.com and click on the link to sign up. You can then follow our step-by-step tutorial to install it.
The preview version of Windows 10 for smartphones won't be released until some time in February, but everyone on the Insider Program will get an alert by email when it's ready to download and install on your Windows Phone.