RQP is broken from version 1.5.+ Moodle onwards. That's why I want it working again. Gustav says it should work again in 1.6 final release. I hope so, it has something to do with the SOAP connection.
RQP is a XML dialect that could be used in the quiz module for remote questions. RQP can communicate with a RQP enabled server. STACK is a RQP enabled program. The RQP dialect works much the same as the XML used in STACK itself.
I haven't found any time to make an English version. I would love to get RQP and thus feedback in the quiz module for maths questions, working again.