A genetic distance measure for aligned sequences
XMas is part of the Japsa package. It, together with its source code, can be obtained from https://github.com/mdcao/japsa.
Detailed documentation of XMas are in http://japsa.readthedocs.org/en/latest/tools/jsa.phylo.xmas.html
A manuscript describing XMas is under review. Please check this page again for a citation.