MIT App Inventor is not available for Windows but there are some alternatives that runs on Windows with similar functionality. The best Windows alternative is Android Studio, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to MIT App Inventor and eight of them are available for Windows so hopefully you can find a suitable replacement. Other interesting Windows alternatives to MIT App Inventor are Basic4Android, AppyBuilder, CCode and AppConvertly.com.
Android Studio is not an online platform and uses Java as a programming language instead of the block builder of the App Inventor.