knitted mathematical models
It seems my grandma was probably good at math without really knowing she was good at math! (she could simply look at you and knit up a sweater without so much as a pattern) According to this article in Science magazine on the relationship between knitting and math,
Mathematics has long been an essential tool for the fiber arts. Knitters and crocheters use mathematical principles—often without recognizing them as such—to map the pattern of a cable sweater, for instance, or figure out how to space the stitches when adding a sleeve onto a jacket.
The mathematicans featured, Hinke Osinga and Bernd Krauskopf, will be coming out with a book in the spring called Making Mathematics with Needlework which will contain patterns and mathematical discussions of 10 craft projects. (via Boing Boing which also has a few links to some neat projects you can make).
UPDATE: The mathematicians are actually not involved with the book but there’s more info on it here.