aimed at supplementing .NET framework XML processing functionality available through the System.Xml namespace and related namespaces such as System.Web.Services. Mvp.Xml project currently provides .NET implementations of EXSLT, XML Base, XInclude, XPointer as well as a unique set of utility classes such as XmlSerializerCache, IndexingXPathNavigator, SubtreeXPathNavigator, XPathNavigatorIterator, XslReader, MpXslTransform and tools making XML programming in .NET platform easier, more productive and effective.
Also take a look at the related project SAXON.NET, "an effort to convert the existing Java-based code of the open-source Saxon processor (8.x-B) to the .NET platform". If you need a client-side XQuery implementation that runs in the .NET environment, or you need an XSLT 2.0 implementation sooner rather than later, check this out. Hmm, I see that Michael Kay himself (the developer of extremely the well-regarded Saxon XSLT / XQuery implementation) is now a project admin. I'll assume that's a vote of confidence!
We in the MS XML team greatly appreciate the work the MVPs and other contributors to these projects have done to supplement the core technologies we develop, and encourage you to take a look.