Widerhall is a mailing list system written in Java. It allows to maintain a set of mailing lists with the option to make (some of) them publicy subscribable.
Widerhall is very lightweight, as does not include a full email server stack.
Compared to other mailing list systems, widerhall is very lightweight:
It contains not mailserver stack. It does not even require you to set up a mailserver!
Widerhall works by just letting you set up any IMAP/SMTP enabled email address with a provider of your choice. It then connects to the inbox of you selected email address and watches for incoming messages. Upon message reception, it forwards the message to all subscribers of the mailing list.
That's it.