Arrow
A list server that allows a user to manage interactive mailing list discussions on a PC. [Windows]
http://www.jadebox.com/arrow/

Mailman
Software to manage email discussion lists. It gives each mailing list a web page, and gives users options such as subscribe and unsubscribe over the web [Unix]
http://www.list.org/

ListSTAR
Discussion lists, newsletters, email on demand [Mac]
http://www.liststar.com/

eSquire
Web-based system. Features autoresponders, integrated support for MHonArc and HyperMail as well as Banned user support.
http://www.gamerz.net/esquire/

Dada Mail
Easy to use open source mailing list management software which operates on any web server that uses CGI scripts. Formerly called Mojo Mail.
http://mojo.skazat.com

JergoBlatz
Play-By-E-Mail mailing-list server. Automates turn-based games such as VGA Planets and provides a forum for the players of those games. It has an immediate mode which allows games such as tic-tac-toe and rock-paper-scissors to be played without waiting for a cronjob to run.[Unix]
http://www.cc.utah.edu/~nb3367/

Ecartis
Open source GNU mailing list management software. It has a many similarities to Listserv which was one of its inspirations. [Unix]
http://www.ecartis.org/

Macjordomo
Macintosh based list server. It can be used in combination with any POP3/SMTP server [Mac]
http://macjordomo.med.cornell.edu/

TinyList
A mail list manager written as a suite of modules. [Perl]
http://www.tinylist.org/

Indexsoft Intuitive Mailer
A mailing list manager [Perl]
http://www.indexsoft.com/intuitive/

MailList Controller
Designed to send out personalized messages, manage multiple mailing lists, newsletters, campaigns, e-zines, announcements, support and group mails.
http://arclab.com/products/amlc/index.html

DOLIST
Stand alone mailing list server software.[Windows]
http://software.dolist.net/

EZMLM
High-speed mailing list manager for qmail. Lets users set up their own mailing lists within qmail's address hierarchy.
http://cr.yp.to/ezmlm.html

LISTSERV
Manage and control e-mail lists, newsletters, discussion groups and direct e-mail marketing campaigns. Free version available for non-profit organizations. Multiple platforms.
http://www.lsoft.com/products/default.asp?item=listserv

Advanced Maillist Verify (AMV)
Verifies the validity of emails in databases, address books and mailing lists the email server addresses are extracted from the DNS. Supports the Socks5 proxy protocol, for use within a local area network (LAN). [Win 95/98/Me/NT/2000]
http://www.mailutilities.com/amv/

eMailer2001
Manages mailing lists, their members and has templates for pre-written messages and filters for the automatic processes. Includes a scheduler and spam checker.
http://www.emailer2001.com/