An MIT project to create a reliable mesh network by giving (selling?) wireless access points and roof mountable antennas to people around Cambridge.
Drawbacks are that people need to install an antenna on their roof, but this pretty much unavoidable unless nearly everybody in the city had an access point.
While I was living in Madison, I considered signing up for Mad City Broadband, which was a more structured commercial endeavor to provide wireless access. However, in my building, reception was sketchy so I didn't go with MCB. The antenna on the roof could have solved the problem, but I didn't have roof access in my apartment building. This seems like a flaw in the roof mounted antenna solution.