The current stream of XmlSchema releases is the 1.4.x branch. In subversion, the source of this branch is https://svn.apache.org/repos/asf/webservices/commons/branches/modules/XmlSchema/1_4_X_BRANCH.
This code is compatible with JDK 1.4 and maintains supports various other components of the Apache Web Service project with similar requirements. In general, the only changes made to this branch are defect fixes and performance improvements.
The next major release anticipated is XmlSchema 2.0. The source code for this effort is on the trunk: https://svn.apache.org/repos/asf/webservices/commons/trunk/modules/XmlSchema.
This code requires JDK 1.5, and attempts to provide a cleaner, more consistent, and simpler API. There is no firm schedule for this effort.