On everybody smartphone there are a lot of apps downloaded from an app store. There apps are build for a specific platform and distributed through a managed selling channel. This works well, but is not really the way the internet worked in the past few decades.
Modern browser allows you to “install” them, but it’s more a link placed on your home screen, and also use them when you’re offline.
But for webapps there is no app store and they are difficult to find, but now there is Appix, the global webapp directory, where you can browse through webapps presentations and find that one you need. Give Appix a try, register and review your favorite webapps.