Notes Font allows you to change the font what do you see in the native application of Notes of your iPhone, you can choose the font and also the size. It brings many types and some are very good on our devices.
It is configured from Settings, it does not add any icon to the Springboard.
You can download it by 0,99$ en Cydia.
You need to have done the jailbreak.
Very good but the best thing is that they had made that same thing more complete with the notes in the system, in the entire iPhone, including the power to change even the size of the battery etc, but it is a good start