Basically, XBuffy (and Xmultibiff) is a XBiff-type program with a lot
of new options.  With XBuffy you can watch multiple mailboxes.  When
new mail arrives, you can have a pop up window showing the From: and
Subject: lines.  You can also set it up to launch your favorite mail
reader when you click on a box.  Currently, xbuffy is only capable of
watching mailboxes with the standard mailbox format (messages separated
with a From line).