This paper about "Sensitive Couture for Interactive Garment Editing and Modeling" is amazing and the source code is available (but not with an Open Source license as far as I can see). It is published at ACM Transaction on Graphics, Proceedings of SIGGRAPH 2011 by Nobuyuki Umetani, Danny M. Kaufman, Takeo Igarashi, and Eitan Grinspun. This is the future of pattern making.
Abstract: We present a novel interactive tool for garment design that enables, for the first time, interactive bidirectional editing between 2D patterns and 3D high-fidelity simulated draped forms. This provides a continuous, interactive, and natural design modality in which 2D and 3D representations are simultaneously visible and seamlessly maintain correspondence. Artists can now interactively edit 2D pattern designs and immediately obtain stable accurate feedback online, thus enabling rapid prototyping and an intuitive understanding of complex drape form.(http://www.cs.columbia.edu/cg/SC/)