The time signature for one measure of Stravinsky's Sacre du Printemps. For this measure--the final measure of "Mysterious Circles of the Adolescents"--Stravinsky wanted a very simple, but also very powerful effect: a series of pulses, with no groupings or subdivisions. To achieve this effect, he simply invented a new time signature. It looks just like I've described it: 11 quarter notes in a row, before it changes to 3/8 or something.
A question often posed to aspiring conductors is this: How is this measure conducted? For 5/4, for example, each measure is divided into a measure of 2 and a measure of 3 (see the Mexican food counting system). But how to subdivide 11 accented quarter notes? The answer, of course, is that you can't. The best way is to just pound the air with your baton 11 times, then move to the next measure.