Phonetix.Net is a C# class-library of phonetic algorithms, implementing Soundex, Metaphone and DoubleMetaphone, with adapters for Lucene.Net. It is a port of the Java-based Phonetix library.
Dr. Micheal Kay: "Saxon 8.7 is the first release to be released simultaneously by Saxonica on the Java and .NET platforms." MDP: Mission accomplished! Saxon for the .NET platform from Saxonica is now available and supported via the http://saxon.sf.net
NLucene is the .NET implementation of the Lucene high-performance, full-featured text search engine written in Java. See http://jakarta.apache.org/lucene for more info on Lucene.