Flipping Typical created by Stuart Robinson is a web based tool that allows you to compare text in the typefaces you have installed.
In a personal note I think it's a very useful tool and I congratulate Stuart for his wonderful work, but not every typefaces installed are displayed (I have only the basic ones)... Maybe I'm being naive but does this happen, due to the browser I'm using or because it's a recent project still in progress?
(via swissmiss)