The STACK system is a computer aided assessment package for mathematics.

In computer aided assessment (CAA), there are two classes of question types. (1) those, such as multiple choice, in which the teacher provides answers and a student selects. (2) those in which the student's answer contains the academic content. For educational reasons, the second kind is usually prefered.

STACK concentrates on student-provided answers which are mathematical expressions. For example, a student might respond to a question with a polynomial or matrix. Essentially STACK asks for mathematical expressions and evaluates these using computer algebra. The CAS establishes various properties of the students' mathematical expressions and on the basis of these properties assigns various outcomes.

A demonstration server can be found here and the software is available under the GPL from the
Sourceforge repository.