Microsoft Web Platform Installer was a tool for automating the installation of products pertaining to the Microsoft Web Platform. It reached end of life on Dec 31, 2022, so don't use it any more.
The Microsoft Web Platform Installer (Web PI) was a free tool that makes getting the latest components of the Microsoft Web Platform, including Internet Information Services (IIS), SQL Server Express, .NET Framework and Visual Web Developer easy.
The Web PI also made it easy to install and run the most popular free web applications for blogging, content management and more with the built-in Windows Web Application Gallery.
It was available from Microsoft. But on Dec 31, 2022 it reached end of life and pulled down by Microsoft.
Modern alternatives are Windows Package Manager/winget, Chocolatey/choco, or others.