XLink
An Introduction to XML Linking, Initial Experiences With an XLink Implementation, XLink Filter Project, xlinkit, XML Linking and Addressing Languages (XPath, XPoin, XML Linking and Style, XML Linking Language (XLink) Version 1.0, XML Linking: An introduction, XML.com: XLink: Who Cares?, XML: XLink and XPointer - Overview
SkunkLink
The SLink language provides a data model and syntax for XML linking, suitable for use in XHTML 2.0 and related languages.
Very Extensible Linking Language Unafraid of Marku
Simon St. Laurent's proposal focuses exclusively on linkbase issues.