Is there an app for Jitsi?

It's called:  Jitsi-Meet

Yes, for iOS and Android
and for OSX and Windows as alternative to the browser:

As alternative to the browser

   - for MacOS/OSX

For OSX: After downloading, right-click on the icon and select "Open". You have to accept the warning and open it anyway. Then at the gear enter a display name and the server ( From MacOS 10.15 please read additionally here.

For Windows: Cancel the firewall warning at the first start, then set the correct display name (otherwise the Windows login name is taken) and server ( at the cogwheel. Admin rights are not required.

Here you can see which version is the latest one: