The rTracker is currently one of the most versatile and customizable apps for self-tracking on the market. Unlike other tracking apps that offer you a fixed set of questions pertaining to only one or two areas (e.g., your body measurements or mood), rTracker allows you to set up your own questions, so you can log any aspect of everyday life, all in one app.
I personally use it to log and store data for about 70 different life variables, including heart rate, weight, mood, social interactions, situational context, etc.. The rTracker also offers a great selection of measurement scales, from boolean (“checkbox”) to multiple choice (“radio-button”) to numeric and text input. I especially love the “sliding” scale, which better represents latent continuum (e.g., mood or happiness) than Likert scales.
Viewing your past records is easy, and you can always go “back in time” and change or add the data point for any given day and time. Another awesome feature of rTracker is shareability: you can export not only data, but also the questionnaire set up so other people could install the same questions on their phone.
The “function” feature of the app allows you to carry out calculations and data manipulations “on the fly”, right in the app. For example, I track my self-esteem on a daily basis using three questions. The “function” automatically calculates the arithmetic average of responses to all three questions in order to get the summary score.
For those of you who are concerned about privacy: rTracker stores your data directly on your phone, and you export it by plugging the phone in the computer and using iTunes.
Finally, rTracker is truly “mobile”: you are not “tied” to the computer, and can log and view your data “on the go”. It also does not require a wireless signal in order to open and use it.