WML made a number of modifications to the GPL licenced Matchbox keyboard, originally developed by Opened Hand Software (who have since been acquired by Intel) for the Sharp Zaurus.
The original code is available here: http://matchbox-project.org/
Our modifications include adding a "Flip" button, an "Exit" button and we added suitable layout for the Tablet project which we were working on.
We also made some small bug fixes to the associated library libfakekey (it was missing a function to clean up memory on exit).
You can download source code to our versions of these two packages here