At the center of the effort is the Seasteading Institute, a nonprofit organization based in San Francisco. Founded in 2008, the group has spent about a decade trying to convince the public that seasteading is not an entirely crazy idea.

Earlier this year, the government of French Polynesia agreed to let the Seasteading Institute begin testing in its waters. Construction could begin soon, and the first floating buildings — the nucleus of a city — might be inhabitable in just a few years.

“If you could have a floating city, it would essentially be a start-up country,” said Joe Quirk, president of the Seasteading Institute. “We can create a huge diversity of governments for a huge diversity of people.”

Mr. Quirk and his collaborators created a new company, Blue Frontiers, which will build and operate the floating islands in French Polynesia. The goal is to build about a dozen structures by 2020, including homes, hotels, offices and restaurants, at a cost of about $60 million...

“I want to see floating cities by 2050, thousands of them hopefully, each of them offering different ways of governance,” Mr. Quirk said.

Human beings have long used floating rafts for habitation; they created them in Mexico in earlier times, perhaps in imitation of naturally occurring floating islands of vegetation.

The earliest really science-fictional treatment of this idea as far as I know is the spaceport from Between Earth and the Moon, a 1930 story by Otfrid von Hanstein.

It was a remarkable island, circular, about half a kilometer in diameter. It rose from the sea, floating on it and fastened to the bottom only by strong anchors. It actually was a huge hemisphere of metal and concrete, open underneath. Above it was shaped to a single perfectly level platform, which rose so high above the water that it was not splashed by the waves. From this platform steps led down to the water all around. On all four sides, ribs several hundred meters long extended out into the sea, forming four harbors which could be used according to the direction of the wind.

(Artificial Island)

"Hey! Look here!"

No answer - nobody - no guard at the shore. There was only the great steel colossus, which held the upright rocket in its spidery arms as if in a tender embrace, rising up alone in the air.
(Read more about the artificial island)

Admirers of Neal Stephenson's Snow Crash may recall Rife's Raft, effectively an independent floating republic.

I'll bet you'd love to visit these other floating artificial island prototypes:

  - Maya Hotel Floating Pyramid Island In Caribbean Sea
  - Lilypad City Floating Island Concept
  - Blueseed Offshore Floating Corporation Ready By 2014
  - Aequoreas Floating Village 3D Printed From Ocean Junk