Quilts is a multiplication pattern viewer, and can help to introduce number theory. It’s simpler to explain if you just use it but essentially it’s a new take on timetables, and good for teaching number patterns. Having written it, just by the patterning I accidentally rediscovered the special case of Dirichlet’s theorem on arithmetic progressions that all primes are of the form mod6 +/- 1, and my maths is rubbish!