Zawinski's Law: Every program attempts to expand until it can read
mail. Those programs which cannot so expand are replaced by ones which
can." Coined by Jamie Zawinski (who called it the "Law of Software
Envelopment") to express his belief that all truly useful programs
experience pressure to evolve into toolkits and application platforms
(the mailer thing, he says, is just a side effect of that). It is
commonly cited, though with widely varying degrees of accuracy.
-- Jamie Zawinski. Defined in The Jargon Dictionary
http://info.astrian.net/jargon/terms/z/Zawinski_s_Law.html