In some awkward formats, like Adobe's Type 1, a single font face is described through several files (i. e. one contains the character images, another one the character metrics).

Using a single font and CSS, you can create countless graphical variations that would normally require the use of an equally countless collection of bulky and non-scalable images.

It syncs with Dropbox, and it has a single beautiful font which makes writing and reading the app fun to use.