Windows 10 is all done and ready to go
This is called "released to manufacturing," or "RTM." And it's a major milestone for the new operating system.
Windows 10 has been in public beta testing via Microsoft's Windows Insider program since October of last year, but the company has decided that it has a final version worth sharing with the world.
This isn't the end of the road for Windows 10. Microsoft has promised that this will be "the last version of Windows," meaning that it's going to keep updating Windows 10 with new features, updates, and patches in lieu of a big-time version with a higher number. They're calling it "Windows as a Service."
Microsoft is working to make the Windows 10 upgrade process as painless to consumers as possible. Windows 7 and 8/8.1 users will have a year to take advantage of a free upgrade to Windows 10, and can sign up to reserve their place in line for that process now - by taking reservations, Microsoft is hopefully trying to avoid an Apple-like server outage as people rush to upgrade their computers.
Microsoft promises that on the official July 29th launch date, there'll be some new computers with Windows 10 already loaded for you, but it may take some weeks for all of the manufacturers to get with the program.
20 years ago, Microsoft released Windows 95 to manufacturers, which is a pleasant coincidence for Microsoft since it's trying very hard to recapture some of the hype that accompanied that product's launch.