CXAN stands for Comprehensive XML Archive Network. If you know CTAN or CPAN, resp. for (La)TeX and Perl, then you already understood what this website is all about: providing a central place to collect and organize existing libraries and applications writen in XML technologies, like XSLT, XQuery, XProc, and schemas.
CXAN is comprised of two different facets: its server, and clients. The server collects the XML libraries and applications, organize them, and make them both browsable and searchable by humans on the website and accessible to programs through a REST-like API. Thanks to its REST-like API, any program can easily integrate with the CXAN server. The CXAN client is an XProc client to be used from the command-line, in order to manage an on-disk repository by downloading and installing packages from the CXAN server. The local on-disk repository manager is expath-repo.