Matt Passmore is a man in a hurry. He is from REBAR, the inventors of Park(ing) Day, and told the Making Space symposium:
The established strategic processes of making urban space are too slow and too cumbersome to keep pace with the rate of contemporary cultural evolution. Recognizing this essential fact, REBAR develops programs of cultural infrastructure that prototype experiences, test spacial ideas and incubate site programs before physical infrastructure is made.
Just about everybody knows about Park(ing) Day, the guerrilla urban intervention that happens every September, where people put money in the meter and roll out the sod and take back the streets. It started in 2005 and is now just about everywhere, and has grown into an open source project. It was such a good idea that people (including San Francisco urban planners) wondered why it shouldn't happen year round; there are 30,000 parking spaces in the city where public space is used to put cars. Why not let people have a few of them? Thus the Parklet was born.
They are now all over San Francisco and a Request for Proposal is out to call for more. REBAR set up the guidelines but they are being designed and built by others as well.
I recently saw one in Philadelphia; unlike San Francisco, these have to be removed in the fall so that the snowplows can work in winter.
In this video, Matt Passmore explains the origin of the Parklet. I apologize for the black bars; It was my first iPhone video and I didn't know how to told the camera.