As often, Microsoft can be confusing when it comes to product naming and line extension; Windows 10 is no exception, so we end up with no less than seven different editions. But for most of us, there'll be only three editions: two for the desktop (plus laptops and some tablets), and one for mobile. Here's an executive summary: Windows 10 Mobile is designed to run on Windows phones. Windows 10 Home edition and Windows 10 Pro edition are designed to run on desktop computers, laptops, and some tablets. Windows 10 Enterprise and Windows 10 Education are editions specialized for large companies and large schools / universities. Windows 10 Mobile edition is reserved for highly portable mobile devices (screen size under 8 inches), and Windows 10 Mobile Enterprise is geared towards large organizations.
Preliminary note: a version of Windows is an actual milestone, like Windows 7, Windows 8, or Windows 10. An edition of Windows is just a flavor of that milestone, like Pro / Professional, Home, Enterprise, etc. Many people talk about "Windows versions", when what they actually mean is "Windows editions".
The two editions you'll want for your desktop computer, laptop, or greater-than-8-inch tablet are Windows 10 Home, pretty much like Windows 7 Home Premium, or Windows 10 Pro, pretty much corresponding to Windows 7 Professional.
Windows 10 Home, the cheapest edition, lacks some features (see "Windows 10 pricing"). Windows 10 Pro, like Windows 7 Professional and Ultimate editions, includes advanced functionality like hard drive encryption ("
BitLocker") and allowing your PC to accessed remotely via Remote Desktop. (There's no "Windows 10 Ultimate edition".) For most non-techies and home users, Windows 10 Home will be perfectly fine, no need to pay twice as much for the Pro version!
You can join a Windows Domain in Windows 10 Pro, but you can't in Windows 10 Home; however, both editions let you access and join a workgroup. Homegroups should also be available on all non-server editions of Windows 10 ("
Windows Server 10"). Briefly, a Windows workgroup or homegroup are like a domain, but very basic, and without support for advanced networking and directory permissions used in large organizations. Homegroups are specifically tailored for home uses, like sharing files, videos, and pictures.
Windows 10 Enterprise will only be available as an upgrade from Windows 10 Pro, not any other edition or version of Windows. This edition doesn't make sense for home users, and probably not for most small businesses either. You'll notice that Windows 10 Enterprise is not even mentioned in our "How to upgrade to Windows 10" tutorial: that's because it won't be an edition of Windows that's available as a free upgrade for the first year. Although anyone -business or individual- can upgrade from Windows 7 Professional or Windows 8.1 Pro to Windows 10 Pro, for free as long as it's done within a year (start counting on July 29th, 2015). But for everyone, upgrading to Enterprise will not be free.
All Windows 10 editions share the same "Windows Store" (like Apple's App Store for Mac OS X and iOS). There are such a thing as "universal apps" which, like Windows 10, adapt themselves to the type of device on which they are used.
All new pocket-sized mobile devices (screen size of at most 8 inches), will come with Windows 10 Mobile pre-installed. For current owners of Windows Phones running Windows 8.1 Mobile, it is possible that an upgrade to Windows 10 Mobile will be offered. This will depend on Microsoft's arrangements with their partners (mobile carriers, chiefly), but also on the hardware limitations of the Windows 8.1 phones in question. Tablets with displays over 8 inches in diagonal will run Windows 8 Home or Windows 8 Pro. (The concept of Windows "
RT", which could not run regular Windows programs, is gone.)
Windows 10 Mobile Enterprise edition, which includes functionality designed for remote management by IT staff, will likely be restricted to large companies, government agencies, and schools / universities. Just like Windows 10 Mobile, it will probably be available as an upgrade, installed remotely or delivered as a download, to Windows 10 Mobile users, and possibly some Windows 8.1 Mobile users.
One feature common to both Windows 10 Enterprise and Windows 10 Mobile Enterprise is the ability to view and download custom apps from a private app store. For security reasons (and fend off industrial espionage, and to keep one's competitive advantage), apps used within the context of the organization should not be visible to outsiders.
Like Windows 10 Enterprise, the Education edition is designed for large scale management of devices, but in this case custom-tailored for academia.
This final edition of Windows 10 is called "
IoT", which stands for "
Internet of Things" (think of target devices like Arduino or Raspberry Pi). That's the term commonly used to describe connected machines talking to one another, or to your smartphone, wirelessly. Windows 10 IoT is similar to Windows Embedded, which runs on specialized industrial systems, ATMs, mining and drilling rigs, etc. (And speaking of industrial operating systems, Microsoft has announced its intention of creating specialized non-IoT versions -editions, really- of Windows 10, designed to run on very specific hardware.) For a bit of fun, see the projects Microsoft has featured on its Windows 10 IoT page.