The folks at Rebar launched a project a few years ago called Park(ing) that converted metered street parking into temporary public parks - feeding the meters for the maximum time allowed and rolling out grass and benches in the spaces.
Well, they've since taken the project national and are asking others to join in the process, by launching Park(ing) Day. Last year's launch in San Francisco and other international cities will be followed up by actions in more cities around the country, led by the Trust for Public Land. For anyone wanting to take part, they have a how-to manual available on their website.
When is this big day, you ask? September 21.