Mailslayer is a program to monitor your mailboxes and tell you how many new messages you have waiting. Its main purpose is to supplement console-based e-mail clients like pine and elm, but it may prove useful for people using other programs as well.
The classical reason. I wanted this program, and couldn't find it (although I found several things that were almost it). I hope other people try it out too, but that isn't essential.
Its functionality (though not its code) is based on earlier programs. The older one is called biff, and the more recent is called buffy. The name is a reference to the latter. I'll leave the rest as an exercise for the reader.
Potentially, all of them. At this point, only POSIX systems. So far, it's been tested on Mac OSX w/X11, Debian GNU/Linux, and Gentoo GNU/Linux.
Currently, you can only get it through Sourceforge's download area. Once it's a stable (or at least a beta) version, I will probably package it as rpm, dpackage, etc. and submit it to various automated services.
The GNU General Public License. The short version: you can download it, modify it to your heart's content, and distribute the changes, as long as you allow everyone else to do the same.
Try mailslayer --help. The information about configuration is wrong at this point, though; just copy /etc/mailslayer to ~/.mailslayerrc and edit it - the comments should help you out. In fact, the information about output is wrong as well (you have to make them Real Live Perl Modules now). Uh, it did say Alpha on the box, right? The docs have been fixed locally, and the updates will be in the next release.
Currently it can read MBOX, POP3, and IMAP. Theoretically it can read maildir as well, but that hasn't been tested. Go ahead and try it out if you happen to have maildirs. Let me know how it goes.
Current output filters (-o) are basic, which will print things in a very basic way (aheh) on your console (this is mostly intended to be fed to other processes), fancy, which will print them in a slightly nicer way on your console (appropriate for humans), and gtk2, which will start up a windowed app if you have the GTK2 Perl bindings. I made a vague, half-hearted gesture at a GTK1 version as well, which you can try with -o gtk. It doesn't work. (Alpha!)
While it would be pretty simple to run it with &, it might be that you want to type your pop or imap password interactively first. The background flag helps with that by, y'know, making it possible. (Yes, I know about fg. Shh. It's funny.)