That build, No. 17618, brings back the Sets feature that Microsoft cut from Redstone 4 earlier this year. Sets is a window-management tool that allows users to group together web pages, documents, files, and apps and work with them in tabs.
In Redstone 4, only a subset of testers got to try out Sets; with this build of Redstone 5, everyone in the Skip Ahead ring gets to test drive Sets. And testers who previously got to try Sets now will see additional new features in the feature, according to Microsoft officials.
In 17618, Sets works with a bunch of Microsoft apps, including Mail, Calendar, OneNote, MSN News, Windows, and Edge. Sets also supports several of Microsoft's own desktop/Win32 apps, including File Explorer, Notepad, Command Prompt, and PowerShell.
There are a lot of fixes to Windows 10 included in 17618 in everything from touchpad gestures, to the overall look and feel. There are also some known issues in the build worth pointing out, especially for those who are interested in using Windows Mixed Reality. Microsoft also is warning that the Microsoft Store may be completely broken or missing with this build (though there is a workaround).