Patternand is a collection of computer programs (written in Python) useful for designing repeat patterns like those found on printed yardage. And for designing rugs, scarves, quilts, linens, etc. The name "patternand" derives from an art movement of the 1970s known as Pattern and Decoration - sometimes abbreviated to P&D.
This site used to host a GPL-licensed version of patternand. The current (much improved) version hasn't been distributed; I'm taking my time about that and thinking through the implications.
catherine at patternand dot org
(also responsible for the morecloth.com textile site)