Naven
Answers
Can you video call without downloading an app?
Yes. Modern browsers carry the technology for voice and video calls built in, so a call can happen on a web page with nothing installed on either end. Naven works this way, as do Google Meet and Jitsi.
The technology is WebRTC, and it has been in every major browser for over a decade. A call opens a direct media connection between two devices where the network allows it and falls back to a relay where it does not, which is why a browser call still works on a restrictive office or school network.
What a browser call gives up against a native app is background behaviour. A closed tab cannot ring unless notifications are turned on, and on an iPhone that requires adding the site to the Home Screen first. For a call you are expecting, none of this matters.
The practical advantage is who you can reach. A person on a managed work laptop, a library computer or a school Chromebook cannot install anything — a link that opens in the browser they already have is the only thing that reaches them.