Whats your single most used app?

I have to say, my most used app is (Memo) came free with the phone. I have it, or a shortcut to it on my Homescreen/Desktop and use it nearly every day to remember things. Soon as i think of somet to do, on the memo it goes. Just got to remember to open the app, but as it's on the homescreen, i see it soon as. :) Priceless!!
Probably just me getting old and loosing my memory or 20 years of frying my head with stimulants. :)