Any suggestions for an easy to use taxi app in Italy (I gather Uber will not work). We will be in Venice (water taxis?), Tuscany near Siena, and Rome.

I think you can use Uber in Rome and Milan currently but it's the premium Uber like Uber Black so more expensive.
A quick Google found a taxi app called FREE NOW.

In Venice it's pretty easy to walk almost everywhere and use the vaporettos. (like taking the bus only on the water)
We took a water taxi to our hotel once in Venice, arriving through the water door which was very cool and then a water taxi to the airport when we departed. The boats are beautiful and you feel like you are in a Bond movie.
I found a site called gotovenice.com that lets you order a water taxi. Usually hotels will call one for you or you can just go to a water taxi stand.

Uber in Rome is a joke - the local taxi drivers prevailed to make it difficult for uber to compete. The lowest cost uber service is not available, and uber has significant reliability problems (e.g., lack of drivers, cancelling a trip after having accepted it or just not showing up.) The Free Now app worked OK for us so we used it until one of the friendly Roman taxi drivers said they prefer the it Taxi app as the money stays in Italy while Free Now is based elsewhere.

that is super helpful all, thanks. I'll get the It.taxi app today