CXTM is defined in ISO 13250-4, that is, part 4 of the Topic Maps standard. It's an XML syntax for topic maps, but not one intended for interchange. (XTM takes care of that.) Instead, CXTM is meant to be used for software testing.
CXTM is a published International Standard. It was published in February 2009.
The following CXTM implementations are currently known:
The current editors are Lars Marius Garshol, professor Jaeho Lee, and Motomu Naito. Feedback can be sent to them or to the topicmapmail mailing list.