iPhone and iPod touch: Commit is a simple app that keeps you committed to a daily task. If there's something you want to do every day so you form a good habit or get the practice you need to be great, this app can help you get there with a nicely-designed, simple interface and helpful reminders.
The way Commit works is pretty simple. You launch the app to find an unfinished sentence: "I will ______ every day." Fill in the blank, then tell Commit when you want to be reminded about this activity, and it will do just that. Whenever you complete this activity each day it'll fill in a slat on your progress bar. If you miss a day, that slat will remain empty, forever reminding you that you didn't do your task.
If you're familiar with the Jerry Seinfeld productivity secret, which operates under the same principles (but with a calendar), you know how this works. Although I personally prefer to use a physical calendar because I like the process of checking off a mark and always being able to see my progress, this is a great little app if you'd rather handle your daily task digitally.
Commit costs $0.99.