Jellyfish is a online assessment program written by NathanScott and ProfessorStone, among others. It's used in ["IntroductionToMechanicsAMEC1001"] and as the basis for FlyingFish. It serves Java applets to the client which contain problems to be solved.
At one point some students studying E101 discovered that one could press ? and enter and the answer would be revealed. This feature was originally intended for tutors to use, as they could bring up a ? button on the interface somehow, but it functioned by the input field instead of making a direct call. This has now been fixed.
Additionally, since it's client-side Java it's not too hard to disassemble it to reveal the algorithm used to generate the problem, which is often sufficient information to work out the answer.