Unfortunately, SharePoint Server 2019 and Project Server 2019 previews aren't available yet. Fortunately, you can actually read through the SharePoint 2019 reviewer's guide, thanks to Microsoft leakster WalkingCat. If your business is subscribed to Office 365, then you should have all of the new features in these products already, or at least most of them. Office 2019 is bringing features that subscription users have been receiving as a service, and putting them in a perpetual license. Office 2019 should be available later on this year. Update: SharePoint Server 2019 preview is now available.