I have found references to SharpNLP (a port of the Java-based OpenNLP), and Antelope by Proxem. I'm looking to create a full parse tree of a sentence (part-of-speech tagging), along with name-finding for dates/times and locations.
The SharpNLP library appears to be inactive since 2007, and it appears that the Antelope library was last updated in 2009. The former is LGPL, the latter appears to require a commercial license but the installer self-describes the license as "underspecified".
Is there a modern NLP library for .NET? Is there a better platform choice for NLP? (it's more important to me to have a great NLP implementation than to stick with a platform choice).
Here is a blog about embedding NLTK in C#: http://blog.samibadawi.com/2010/03/open-source-nlp-in-c-35-using-nltk.html .
But I would move to Python.
Go NLTK.