ooh string designs. Our book introduces these as straight line patterns. Minimath projects has very affordable card supplies and patterns that even I, the inartistic math teacher, can follow. I made one example of each for the students to see what they look like. Really, only card 3 is very mathy, since it uses coordinates. However, one has to follow instructions in order, which is a challenge in itself for my students.
I use crochet thread and tapestry needles, to minimize the eye-poking-out possibilities in the classroom. The last time I had geometry, 5 years ago, some students liked these, and made them as christmas gifts. Not bad for the mean Jewish math teacher.