I first bought my iPhone specifically so that I could track my mood. After trying all of the available self-tracking / data-entry apps I couldn’t find one that didn’t feel like a chore to use.
So I built me own: Zen Log (iTunes preview)
It’s optimized for numerical input (no text) and is designed to minimize mental friction while using it. The input method is a long-press (tap and hold) and you do this after scrolling to the selected log and scrolling to the value you want to log. So there are only two modes: scrolling, and a long-press.
This makes the app effortless to use and requires minimal cognition and barely any precision from your fingers - so you can use it while walking, talking, or with your non-dominant hand.
*Basically, for me, it took lifelogging from being a chore to being something I barely think about. *
I use it to track my mood, sleep quality, pulse rate, temperature, and whenever I sneeze.
While I think the iPhone is a great tool for capturing/logging data, I don’t think it’s a good tool for any serious plotting or analysis. So there’s no charting within the app. Data is exported by emailing a CSV file.
Hope you find the app as useful as I do.
Note that the first log is free and fully editable and functional. Creating additional logs requires a one-time in-app purchase.
PROS: Fast, intuitive, gets out of your way, versatile.
CONS: No text entry, no charting, no server syncing.