There is a place called Slab City, East of San Diego, California, where people stay for free as long as they want. It is an abandoned military base, which now attracts those looking for one of the last free places, or seasonal snowbirds.
They have a library, a community center, an outdoor music theater, and tons of social amenities. I visited it in 2009, and found people to be very friendly. The only problem is that, during the summer, it is unbearably hot. It attracts tons of Canadians and mid-westerners who only stay for the winter.