Recommended phone apps

It’s The Fork.

Citymapper (for public transport in cities)

Tripit (to keep all your reservations in one place.)

Google Maps (for directions)

Weather app

WhatsApp - also for making reservations and communicating with air bnb hosts - they like to use wifi instead of data.

Trenitalia
Italo Treno
the airlines you’re flighting on
CheBato? (Venice vaporetto)
Google Translate

I'd dump from the Trenit! app and go with the apps from Trenitalia and Italo. Trainline can also be useful.

The vaporetto app is CheBateo?

Chebateo for vaporettos in Venice.

Taxi cabs in Rome use the ItTaxi App, the app of the Italian Radio Taxi Union.

In Florence they dumped ItTaxi to protest against the fact that ItTaxi reached an agreement with Uber that permits Uber users to utilize Uber App to summon taxicabs through ItTaxi. As a result the two taxi cooperatives in Florence use the following apps:
Taxi Move
AppTaxi
I uploaded them both, but I had a hard time registering using my US based telephone, so I simply called (or had the hotel call). Maybe you have better luck. If you stay in the city center, you will need a taxi in Florence only to go from the airport or the train station to your hotel (and viceversa). Florence city center is very small, so you will walk everywhere.

Keep the Trenìt! app as it gives you real time departures and delays, and even when you’re on the train you can see the next station with real expected times of arrival.
Be sure to have the apps and phone nos. of every airline you are travelling on.
Booking.com and a couple of other hotel apps, in case you get stranded and need different accommodation in a hurry.
I don’t know where you live, but the government app for your home country is very useful as it will give you contact info for embassies and consulates in places you travel to.
Google Translate.
Airport apps are good to have as they have maps of terminals.
FlightView and Flightaware.
Can’t think of any others at the moment.
Good to be fully prepared!
.

ilMeteo for weather.