Ruffus is a Computation Pipeline library for python. It is
open-sourced, powerful and user-friendly, and widely used in science
and bioinformatics. Ruffus is designed to allow scientific and other
analyses to be automated with the minimum of fuss and the least effort.

Please cite Ruffus as: Leo Goodstadt (2010): Ruffus: a lightweight
Python library for computational pipelines. Bioinformatics 26(21):
2778-2779

Optional requirement: graphviz