Right now, Build 10240 of Windows 10 is rolling out to both Fast and Slow rings. Windows Insiders today are able to download and install what could end up as the RTM version of Windows 10. Microsoft isn't willing to put the RTM stamp on today's Build, but there's a couple pieces to this release that make it a good candidate.
What's interesting about this Build:
The Desktop watermark has been removed
It is only available through official release channels (i.e., Windows Update)
Mary Jo Foley says that her sources revealed that this actually *is* the RTM Build, but we'll have to wait to see to be positive. Anything and everything can change, and usually does. Still, we are extremely close to a July 29 release of the Windows 10 upgrade, so this one is definitely worth an install.
To get Build 10240, you can wait for Windows Update to do its job and install it automatically, or you can force the update by opening the Windows 10 applet for Windows Update and initiate a "Check for updates" manually. A Microsoft account, of course, is required to receive Build 10240.
Over the next couple weeks, Microsoft expects to deliver additional updates through Windows Update and in the new Windows 10 Store, so watch for those.