WinROT13 is a freeware ROT13 and ROT47 scrambler/disscrambler for Windows.
ROT13 was designed for use in the newsgroups as a means to "hide" the content of postings. Another way ROT13 has been used is scrambling e-mail addresses in the contents of news articles, making it difficult for Internet spammers to steal the addresses.

If your newsreader does not support ROT13 or you want to use ROT13 in eMail, then you need winRot13. Note that ROT13 is not secure; it is not inteded to be so and can not replace PGP.