Microsoft has launched the preview version of the .NET Framework for download and try it. This .NET Framework 4.8 is a preview version and more or less close to the stable version and includes several accessibilities, smooth performance and reliability. This release is only available for Windows 10 version 1809, Windows 10 version 1803, Windows 10 version 1709, Windows 10 version 1703, Windows 10 version 1607, Windows 8.1, and Windows 7 SP1 as Windows client.
As Windows Server, this .NET Framework 4.8 Preview Version will work on Windows Server 2019, Windows Server version 1803, Windows Server version 1709, Windows Server 2016, Windows Server 2012, Windows Server 2012 R2, Windows Server 2008 R2 SP1.
According to Microsoft …
This build includes an updated .NET 4.8 runtime as well as the .NET 4.8 Developer Pack (a single package that bundles the .NET Framework 4.8 runtime, the .NET 4.8 Targeting Pack and the .NET Framework 4.8 SDK). Please note: this build is not supported for production use.
So if you want to just try this .NET Framework 4.8 Preview Version build 3734 then you can download it from these bellow links