There are lots of apps on the App Store for tracking numbers, like your weight, your golf score, and how many hours you've worked lately, but Dayta serves as one solution for all of those. You can simply create stats however you like, and then track them to your heart's content. You can export them out to CSV files, or you can browse and visualize them directly within the app, doing whatever you want with the raw data that you collect from day to day.
Plus, the app was just revamped, so now you get full Retina Display compatibility, lots of new enhancements and performance updates, and even the ability to tweet any data that you happen to input. That seems like an excellent deal for US$1.99. Of course, if you already have a few apps set up for tracking the relevant data in your life (like apps for your calorie intake or your car's gas consumption), that's a fine way to do it. There are definitely apps on the store that will allow for more customization and more specialized tracking than Dayta. But if you enjoy pulling in a bunch of raw numbers and have a few spare stats to check, Dayta might be able to help.