Wikipedia
Fetchmail
Fetchmail is an open source software utility for POSIX-compliant operating systems which is used to retrieve e-mail from a remote POP3, IMAP, ETRN or ODMR mail server to the user's local system. It was developed from the popclient program, written by Carl Harris.
Its chief significance is perhaps that its author, Eric S. Raymond, used it as a model to discuss his theories of open source software development in a widely read and influential essay on software development methodologies, The Cathedral and the Bazaar.