Calabash is an implementation of XProc: An XML Pipeline Language.
See the Calabash project status page for more details.
You can download Calabash and/or read the (very little bit of) documentation.
If you're interested in tracking the development of XML Calabash, you might be interested in:
Following the discussion on xproc-dev (archived at lists.w3.org and MarkMail). XProc-dev is a general XProc discussing list, not limited specifically to XML Calabash.
Following the code development in Subversion.
Following the issues list.
You can even follow xmlcalabash on Twitter or identi.ca, if you want. Or xproc on Twitter or identi.ca, for more general XProc tweets.