Check out 596 Acres.
Excerpts from their About page:
Hundreds of acres of vacant public land are hidden in plain sight behind chain-link fences in New York City, concentrated in neighborhoods disproportionately deprived of beneficial land uses [emphasis mine]. We are building the tools for communities to open all these rusty fences and the opportunities within them to improve the areas they live in.
596 Acres creates tools to help neighbors find the lot in their lives by:
(1) making municipal information available online and on the ground (e.g. by placing signs on vacant public land that explain a lot’s status and steps that the community can take to be able to use this land);
(2) providing education about city government and ways to participate in decisions that shape neighborhoods;
(3) assisting communities with legal support and campaign-development on land use issues;
(4) maintaining networks that allow communities to share knowledge and relationships with decision-makers;
(5) working with groups after they get access to land to build sustainable community governance as they become stewards of a public and inclusive resource; and
(6) advocating for municipal agencies to increase participatory decision-making surrounding public resources.
Turns out the local governments in the US love to fence public lands as well.
It’s up to us, the public, to demand our public land for public usage, instead of letting them sell off our land to private developers.