This is a simple, generic interface for making applications which use the mouse and keyboard. These events are transformed into nicer datatypes, making it easy to ignore the details of the backend's event datatypes. Coupled with a backend-independent rendering system such as diagrams, this allows for backend-independent applications to be written.
The name "toy" comes from the "toy framework", a part of the lib2geom library. It's used in building "toys" demonstrating the features of the library. This is a different variety of "TDD" - but instead of tests, it's toys! We found that building little demos to be a nice way to drive initial design / development.
If you want to build the latest repository versions of the toy packages, use toy-sources, or manually fetch / build the repositories.