Lambda the Ultimate

One of the gems squirreled away on Oleg's site is "Makefile as a functional language program":

"The language of GNU make is indeed functional, complete with combinators (map and filter), applications and anonymous abstractions. That is correct, GNU make supports lambda-abstractions."

Although I've classified this under Fun, Oleg exploits
the functional nature of Make for a real, practical application:

"...avoiding the explosion of makefile rules in a project that executes many test cases on many platforms. [...] Because GNU make turns out to be a functional programming system, we can reduce the number of rules from <number-of-targets> * <number-of-platforms> to just <number-of-targets> + <number-of-platforms>."

See the article for a code comparison
between make and Scheme, and check out the Makefile in question.