REXML-Sharp is an XML library for C# that makes working with XML simpler and more performant than alternatives. It is a port of JSXML which included REXML, an regular expression-based XML parser written in JavaScript and released under LGPL license circa 2000 that outperformed any other XML parser available for browsers at that time.
It is currently in alpha state because though it functioned in prior versions of .NET, it does not work properly in the more recent versions (port was around 2003 and was working with .NET versions up to 2011).
More documentation coming soon, but a look at sourceforge.net/projects/jsxml can give more indication of the intended functionality, and the interface for all classes is very simple (which is the point, a whole lot simpler than the W3C DOM and others).