What is the name of the extensible web server software created by Microsoft?

The extensible web server software created by Microsoft is known as Internet Information Services (IIS). IIS provides a powerful platform for hosting web applications, and it integrates well with other Microsoft technologies, making it a popular choice within the Windows Server environment. IIS supports various web development frameworks, offers security features, and provides management tools that enhance performance and reliability for web applications.

The other options represent different web server software: Apache is a widely used, open-source web server primarily for Linux environments; Nginx is known for its high performance and scalability, often serving as a reverse proxy server; and Tomcat is primarily used for serving Java applications. However, none of these are created by Microsoft or are specifically designed to integrate fully within the Microsoft ecosystem like IIS. This makes IIS a unique solution tailored for users and developers working within Microsoft's technology stack.