Metricom Ricochet is a wireless mesh technology that was deployed in San Francisco and the Bay Area in 1997. They deployed relay radios on lamp posts and you could roam around the area while maintaining contact through a device that hung on the top of your laptop screen. If more people started using the device in a certain area, they deployed more radios. If you moved to the edge of a service area, they would extend it within a couple of days.
The service reached as far south as my office in Redwood City on the border with Atherton where one of my colleges used it to keep in constant IRC contact with his friends.
Some URLs for the old Ricochet which was NOT wi-fi and is not the same as the new revived Ricochet company.