Milan’s municipality offers free outdoor WiFi to residents and visitors – It is continually evolving and the areas that are covered (hotspots) are getting larger and larger.
There are no limits to how much data you can use per day when you are within reach of Milan’s excellente OpenWiFi.

You can log in with your email address and a password you create yourself. Read more here
The app WiFi Map tracks when you are within range of a WiFi hotspot.