Except where it explicitly says otherwise, the material found on the JXCL Web site is made available under the XLattice License, which you may review by clicking here.
Certain material, all of which is documentation in one form or another, is marked as being available under the Artistic License, a copy of which is here. In all such cases the copyright holder is named and reference is made to the Artistic License.
Both of these are Open Source licenses. See Open Source for more information on various types of open source licenses, including BSD-style licenses like JXCL's.
The JXCL distribution includes jar files for other open source software. These are covered by their own licenses, which should be consulted.