pop3ml is a program to manage mailing lists and newsletters without a local SMTP server. It requires only a simple POP3 email account. It's highly configurable by users. You can subscribe or unsubscribe simply with email messages. There is optional subscription and unsubscription confirmation, subscription moderation, message moderation, digest message mode, parent/children list management, mail scheduling to postpone or repeat a message, a mail filter (with a procmail-like syntax), a message queue for unsent messages, message size check, a command to retrieve messages, bounce detection, message header management, black/white/allow/deny lists, and other functions. There is also a program to test list settings without sending any messages and another program to view and search through stored messages. You can configure it with programs like phpMyAdmin.
pop3download is a script that downloads e-mail from a POP3 or IMAP mailbox. It was originally created to work around certain fetchmail bugs, and now works as a very limited and simple alternative to it. It can keep files on the server, force CRLF line endings, poll at an interval, and pass mail through an MDA for filtering.