There are two implementations so far: jsonwidget-python, a terminal window implementation suitable for editing forms via ssh or in a local terminal window, and jsonwidget-javascript, a client-side JavaScript library that generates a basic HTML form interface in a Web browser. Application designers using one of these libraries have the option of providing a schema, limiting the input to a subset of valid JSON compatible with whatever application is actually consuming the JSON, or using a provided permissive schema that allows any valid JSON. The libraries are capable of dynamically generating a form is using nothing more than a schema and a JSON file as input.

PPA: https://launchpad.net/~robla/+archive/ppa
  on Karmic: sudo add-apt-repository ppa:robla/ppa

More details can be found on the website: http://robla.net/jsonwidget