OpenNewsletter is a free & open-source newsletter/mailing-list manager written in php developed by Self Exile. It does not require a database. You just need to put it in your website and its running!
I am Sohail Abid code name Self Exile, the developer of OpenNewletter. I created it because I like beautiful but simple things. You can visit my home page at www.selfexile.com. And the home page fo this software is now: www.selfexile.com/projects/opennewsletter. My email address is self.exile at gmail.com and my sf project page is sourceforge.net/projects/opennewsletter