XLinkFilter is licensed under the Mozilla Public License, and source code is readily available.
Contributions are welcome.
The motivating philosophy behind this project is 'keep it simple' - application developers shouldn't need to know very much about processing links to use them in their programs. Support for most of the XLink spec is provided, except for attribute remapping and extended link groups. I'm hoping that all the turmoil over namespaces has provided a solution for attribute remapping, and support for extended link groups is under development. Because of its SAX orientation, XLinkFilter is probably most appropriate for small applications where building a full DOM tree is unnecessary, but I'd love to hear if anyone uses it for something larger. Source code, examples, and more description and documentation are all available there.