I don't read much about the Tuscan coast on this travel forum. Can anyone recommend small, quaint towns along or near the coast that are not too busy with tourists in mid September?
Traveling there by train or by car?
Porto Santo Stefano is charming and just offshore is Isolo Giglio, reachable by ferry. We enjoyed off-season time there one May, Memorial Day weekend if I am remembering correctly. The high-season is July and August. Weather is still great in September.
Traveling by car
Forte dei Marmi
Viareggio
Donoratico, Cecina, and just inland, Castagneto Carducci and Bolgheri. Farther inland in forested hills with twisty roads, Suvereto, Massa Marittima, and pretty much any village you come through on those roads.
If you have a car, then the choices are many. North to south:
On the water:
Castiglioncello
Rosignano Marittimo
Populonia (on top of a hill, but virtually on the water)
Castiglion della Pescaia
Talamone
Porto Santo Stefano
Porto Ercole
Near the coast:
Bolgheri
Castagneto Carducci
Sassetta
Campiglia Marittima
Scarlino
Capalbio
Happy research on the above.