Marker (Just marks the current date and time with a tap.)
Duration (Such as lap times.)
Predefined values (You can set values and choose.)
Multiple values (Any two or more of the above, but available only in the pro version)
Once you set up the trackers you want, it's just a matter of firing up the app and keying in the input. You could use it for anything from tracking things you lent to a journal of your wins. When you want to review it, it's available as a calendar view, as a list of statistics, or a bar graph.
KeepTrack Pro ($1.99) also lets you add reminders to fill those trackers, as well as other features like the aforementioned multiple values.