What are good apps for rationalists?

The smart­phone world is rel­a­tively new, so I sus­pect there are amaz­ing (yet some­times un­known) apps that can help var­i­ous as­pects of our lives. I can­not think of a bet­ter dis­cus­sion place for this topic. So,

Which app help you op­ti­mize life?

Is there an app you keep search­ing for in vain? (though it might ex­ist!)

For me (I was search­ing for both apps for months!! un­til they were fi­nally cre­ated):

Anki, A flash­card mem­o­riza­tion app with many use­ful fea­tures.

[From the link] Anki is a pro­gram which makes re­mem­ber­ing things easy. Be­cause it is a lot more effi­cient than tra­di­tional study meth­ods, you can ei­ther greatly de­crease your time spent study­ing, or greatly in­crease the amount you learn.
Any­one who needs to re­mem­ber things in their daily life can benefit from Anki. Since it is con­tent-ag­nos­tic and sup­ports images, au­dio, videos and sci­en­tific markup (via LaTeX), the pos­si­bil­ities are end­less.

Sim­ple Counter Wid­get, A counter wid­get. Sounds sim­ple, but it’s amaz­ingly helpful.
I use it as a tool to bet­ter my­self. Every time I eat my gum (an an­noy­ing mostly un­con­scious habit), the gum-eat­ing-wid­get is in­creased by one. Be­cause the wid­get is so ac­cessible, I rarely cheat. This gives the habit im­me­di­ate nega­tive feed­back, and al­lows me to check im­prove­ment over time. (Also my desk­top looks cool, with many in­trigu­ing num­bers pop­ping from ev­ery­where)

(less in­ter­est­ing: Record Mic and Call—which in­cludes a use­ful record­ing wid­get, and Waze—which is amaz­ing but well known GPS app (at least here))

please share to make this in­ter­est­ing :)