TrenItalia App: If you are planning to do any travel by train in Italy, which from my experience traveling from Milazzo to Rome, was very efficient and comfortable, you will find convenience in having their app downloaded on your phone. Even if you are just planning to take the train to/from Roma Termini to the Rome Fiumicino Leonardo DaVinci International, there is an express train (Leonardo Express) that is the least expensive way to get to and from the airport (about 14 Euro one way).
Liberty Lines App: If you are planning to travel to the Aeolian Islands, you will need to familiarize yourself with Liberty Lines. Their app isn’t great, but it is the easiest way to review and book rides to, from and between the islands. They say on their website that you need to check in with the ticket office an hour before your departure even if you bought the ticket prior, but I found that wasn’t necessary. One bag is included with the regular fare. You can add extra bags for a few extra euros, though it didn’t seem like they were too strict in monitoring this.
EasyPark App: This is a great app for finding and paying for parking in Sicily. You will see their pink signs at most of the public parking areas throughout Sicily, even in some of the smaller towns. It takes a lot of the guesswork out of paying for public parking, and the app willl remind you when your time is expiring.