MetaCard was a cross-platform, commercial GUI toolkit. MetaCard included an IDE and had its own language, MetaTalk. From the MetaCard Corporation website: "The MetaTalk language has all the features common to third-generation languages like C/C++/Java but has a much simpler syntax."
All the Metacard technologies are now part of Runtime Revolution ("RunRev"). The only part that Runtime Revolution did not adapt was the GUI of the Metacard IDE. It lives on as the Metacard IDE open source project. It currently exists as a yahoo group, as well as a mail discussion list hosted by Runtime Revolution.