The XAML Toolkit is a collection of tools and libraries designed to enhance the development of applications using XAML (eXtensible Application Markup Language). It provides developers with pre-built controls, styles, and templates that simplify the process of creating user interfaces for applications built on platforms like WPF (Windows Presentation Foundation) and UWP (Universal Windows Platform). By utilizing the XAML Toolkit, developers can save time and effort while ensuring a consistent look and feel across their applications. The toolkit also supports customization, allowing developers to modify existing components or create new ones to meet specific design requirements.