Windows 10 is far from finished, and this preview is still intended just for advanced Windows users who are unfazed by the possibility of running into pre-release bugs. [I'll update this page with installation links when I have them.]
The basic layout of the Windows 10 Start menu is unchanged since the first round of preview releases. This update is cleaner, with much less clutter. And it offers the first peek at Continuum, one of the signature features aimed at easing the transition to touch on hybrid devices. The button in the upper right corner switches the Start menu to a full Start screen.
To date, Cortana has only been available on Windows phones, which means most Windows users aren't aware of what this digital assistant can do. Cortana offers a search interface that can be driven by speech or by the keyboard. You can also ask Cortana to set reminders and create appointments.
It's official: The Charms menu is gone, dead and buried beginning with this preview. In its place is the new Action Center, which slides in from the right and displays notifications from apps, with buttons along the bottom that control useful settings.
This preview release still includes the desktop Control Panel, but this new Settings app is clearly intended to be the long-term replacement for Control Panel. It's significantly expanded in scope from Windows 8.1, and the new design offers a sensible navigation structure.
Here's the new Settings app in action, with significant improvements in the interface for managing wireless network connections.
The new, brighter icons in File Explorer are the most obvious change. Look closely and you'll also see Pin buttons that let you ensure that a folder is always available as well as a useful "recent files" list.
The Search experience in this preview release is much improved over the earlier version, including the eagerly awaited return of email messages in the multi-tab results pane.
The Maps app is an essential part of a mobile device, although it's still useful on a desktop PC. This release, done as a universal app, merges functions that were previously scattered among several apps. It also includes the ability to download maps for offline use.
The new Photos app, which is tantalizingly unfinished (the Albums and folders tabs are both marked as "coming soon" for this release) offers an integrated view of photos in your collection, regardless of whether they're stored locally or in the cloud. The default settings include an auto-fix capability that nondestructively tries to improve photos for display and sharing. If you don't like the fixes, you can undo them easily.
The Windows Store, which handles third-party apps as well as those included with Windows 10, gets a significant redesign in this preview, with the new store getting a prominent Beta label and the old store still available. Note the status indicator that shows 12 updates are available for download and installation. Don't try to apply those updates manually, though; only automatic updates are available in this build.
As with previous Windows versions, you can click Start and begin typing to see a list of apps, files, and Control Panel settings that match your search terms. This edition finally explicitly names what were previously known only as Metro-style apps. In build 9926, Windows 10 distinguishes between Modern applications (universal apps) and desktop programs, which are called Windows applications.
Anyone who has ever been rudely surprised by Windows' insistence on rebooting at an inconvenient time to install updates will appreciate this new option. The system will pick what it believes is a convenient time to reboot, but you can override that decision with your own preferred time.
In this build, the options for backing up files and settings are rearranged yet again. This settings page has a distinctly unfinished feeling to it.