Naven
Glossary
Progressive web app
A website that can be installed like an app, with an icon, its own window and background notifications.
A PWA is an ordinary site plus a manifest describing how it should be installed and a service worker that can run when the page is closed. Installing it costs no app store, no review and no download of a binary — the site is already there.
On Android it is close to a native app. On iOS it is more limited, and notably notifications only work once the site has been added to the Home Screen.
Where Naven stands
Naven is a PWA. Adding it to a phone's home screen is what enables notifications that arrive when the tab is closed, which on an iPhone is the only way to get them at all.