pliMa is a php mailing list application that allows users to easily set up lists as needed, to choose what extra information they would like to harvest when users subscribe, then to select subsets of a list as recipients of a broadcast mail-out. It makes use of the well established phpmailer class which is capable of sending up to 40,000 messages an hour. Sources are released under the GPL licence and are available from sourceforge.net/projects/plima/

I've also been working a lot on a project I call postLog. I've kinda put it on Sourceforge - insofar as it's registered and described, but I haven't put the source up yet - mainly because I haven't cleaned it up for simplicity of installation. Check it out at sourceforge.net/projects/postlog/, and if you're interested in finding out more about it please contact me and i'd be happy to let you have the code.