Earlier this month, Microsoft announced the release of .NET Core 3.1 on their development blog, together with ASP.NET Core 3.1 and EF Core 3.1. The new releases are mostly composed of fixes and refinements over their previous version (3.0). However, these are long-term supported (LTS) releases, which means they will be supported for at least three years.
The changes in .NET Core 3.1 were focused on Windows Desktop development. A number of legacy Windows Forms controls were removed: DataGrid, ToolBar, ContextMenu, Menu, MainMenu, and MenuItem. Support for creating C++/CLI components was also added to Visual Studio 2019 16.4 (Windows only).
Most of the ASP.NET Core updates were fixes related to Blazor, such as preventing default actions for events and stopping event propagation in Blazor apps. While not being officially part of the new release, the public preview of Blazor WebAssembly was also updated. The new preview features include: .NET Standard 2.1 support, iOS13 support, and debugging Blazor WebAssembly apps by attaching the browser processes to Visual Studio.
The most important update for EF Core 3.1 was the reintroduction of support for .NET Standard 2.0. Similarly to the other releases, the primary goal of version 3.1 was to polish the features delivered in the previous version. There were over 150 issues fixed since the previous release. Consistently with the latest EF releases, EF 6.4 was also made available on nuget.org, fixing a small number of issues found in EF 6.3.
According to Microsoft's release calendar, these are the last major versions of the Core products before .NET 5 (expected in November 2020). Blazor WebAssembly follows a separate release calendar: the official release of Blazor WebAssembly is expected to May 2020, and Blazor PWA is scheduled to have previews release with .NET 5.
Visual Studio 2019 16.4 update is required to use .NET Core 3.1 with Visual Studio. .NET Core 3.1 is supported on multiple operating systems, including different Linux distributions, macOS, Windows 7+, and Windows Server 2012 R2+ (a complete list of supported operating systems can be found here).