If you're an everyday user, you'll have to wait until sometime in the 'next few weeks' to get a copy. Only trusted commercial volume customers have a crack at Office 2019 right away. OneNote is still free and available outside of Office, regardless of the platform. Outlook has updated contact cards, support for Office 365 Groups, mentions, a focused inbox and new summaries for deliveries and travel. Excel offers funnel charts, 2D maps, timelines and new functions. PowerPoint has a new roaming pencil case, morph transitions, 4K video export and the ability to insert content like 3D models and SVG images. Word now has a Focus Mode (on Mac) to help you knuckle down on that must-finish report, not to mention a dark theme on Windows, better inking features and accessibility upgrades like Read Aloud. They're not revolutionary, but they could be helpful if you've stuck to Office 2016 or earlier releases.
The company is rolling out Office 2019 for Mac and Windows, giving you a 'subset' of the upgrades that have come to Office 365 ProPlus in the past three years. Just because Microsoft is bent on moving everyone to cloud-based subscriptions doesn't mean it has forgotten about those who want a one-and-done purchase.