You can now download macOS Mojave 10.14 from the Mac App Store. Apple announced at its iPhone XS event the latest version of macOS would be available on September 24th, and here it is.
New features in macOS Mojave include system-wide Dark Mode, time-shifting desktops, Stacks for your desktop files, improvements to Finder (Gallery View, Quick Actions, Complete Metadata), Quick Look to edit files, easier screenshots, use your iPhone to snap a photo to the Mac, Group FaceTime (coming later this fall), new apps (Stocks, Home, Voice Memos), revamped Mac App Store, better security, and more.
Click here to download macOS Mojave in the Mac App Store (5.7GB download). Be sure to have a back up of any critical files before you update, just in case.