Viewport is one of the modules I maintain for Drupal 7. It’s a very small and simple module that does a very specific thing: it allows site admins to specify the values they want for the HTML meta tag that specifies the viewport settings for browsers. It also allows admins to choose the pages in which they want this custom viewport applied.
Back in the day a client required this functionality to embed some browser games that required very specific settings. Nowadays it’s not really common for a site admin to set those values, and developers don’t really require any UI to set them.