FreeCard is a open-source replacement of Apple Computer's HyperCard, which is a Macintosh-only rapid-application development tool.

FreeCard will improve on HyperCard by adding more and even easier scripting languages, integrated color support, support for Macintosh, Linux, and Windows, a MUCH faster interpreter, and whatever else we come up with.

It is currently being written. (I am one of the principal developers)