iOS: Jerry Seinfeld's productivity secret involves crossing off a day on a calendar for each task you complete. Each crossed-out day creates a chain, and you'll quickly find that you'll keep doing your work to avoid breaking it. I've been using this method and it's great, but six months of calendars for four separate tasks takes up a lot of space.
Once you've been checking off boxes on a paper calendar long enough, getting your tasks done every day becomes more of a habit. It's harder to avoid doing them. While I do think using a paper calendar is better in the beginning, as it's always in your face, after you've gotten the hang of not breaking the chain you don't really need that extra motivation. Wonderful Day is an app that can take the place of your paper calendars by tracking your activity from your pocket. You just add the tasks you want to complete, let Wonderful Day know when you're supposed to do them, and check them off when you've finished. It's about as simple as it gets, and you can see your progress in a giant dot grid.
We've reviewed a similar app called Commit, and it's very good, but it's also more expensive. The advantage Commit has over Wonderful Day is that it can remind you to do your daily task whenever you want. While Wonderful Day will remind you, it just happens at a set time every morning rather than a time you choose that can vary by activity. This is a very minor issue, however, and won't matter to most people. Overall, Wonderful Day is an incredibly simple way to keep yourself motivated to form good habits and get things done.
Wonderful Day ($0.99) [iTunes App Store]