You know fetchmail or getmail? You know procmail or maildrop? Well, fdm (http://fdm.sf.net) is basically those two feature-sets combined into one nicely done application. This program was written by the same guy who brought you tmux.
After years of being a WindowMaker (http://www.windowmaker.info) user, I switched to fvwm (http://fvwm.org) at the end of 2005. Since then, this configuration came to be. It emulates my old WindowMaker setup to a certain degree.