It appears to be a driver for UUencoding. All binary files are transmitted over the internet as plain ASCII text and this is normally achieved by MIME encoding them, sending and then MIME decoding by the recipient. This is all done automatically by email programs when sending attachments.
There are other methods of encoding one of which is UUencoding / UUdecoding. It is an older method, but is still supported by some email programs. Eudora, for example, offers MIME, BinHex and UUencode for attachments.