The Microsoft .NET Desktop Runtime is a software component that enables users to run existing Windows desktop applications built with the .NET platform (including Windows Presentation Foundation (WPF), Windows Forms, and Universal Windows Platform (UWP)). It acts as the execution environment for these applications, providing essential services such as memory management, security, and exception handling. 

Key Information

• Purpose: The primary function is to provide the necessary environment for .NET desktop applications to run on Windows. It is not needed for all Windows programs, only those specifically developed using the .NET framework or the modern .NET (Core) platform's desktop components.
• Components: The .NET Desktop Runtime includes the base .NET Runtime, so you do not need to install the latter separately.
• Compatibility: It is designed to work alongside older .NET Framework versions, allowing applications based on different versions to run without conflict.
• Latest Versions: The latest supported Long Term Support (LTS) version is .NET 8.0, and the latest Standard Term Support (STS) version is .NET 9.0.
• System Requirement: If an application requires a specific version of the .NET Desktop Runtime, that version must be installed on the system. Uninstalling it may cause dependent applications to stop working correctly.
• Automatic Updates: For end-users, the runtime is typically installed automatically with Windows updates or when an application that requires it is installed.