The Wikiprep# program is completely written in C# and based on .Net 4.0 . It processes Wikipedia dumps which are available here:
http://dumps.wikimedia.org/enwiki/latest/
It replicates the functionality of the wikiprep project that was originated by Evgeniy Gabrilovich although the output files have a different format.
The program can be found on Github and is licensed under Apache 2.0: