OpenSilver is a free, open-source UI framework designed for building modern .NET web applications using C# and XAML. It supports WPF and Silverlight applications and facilitates seamless transition away from legacy Silverlight technology. The framework ensures 100% code reusability, compatibility with various modern web technologies like Blazor, React, and Angular, and offers an AI-enhanced XAML designer for Visual Studio Code. With OpenSilver, developers can build cross-platform applications that run on any browser and device, preserving the original look and feel of the apps, while significantly reducing the migration cost and time.