iOS: Time tracking apps tend can often be a bit awkward to use. Hours is an app that seeks to change that -- the app only requires a tap to start working.
To track your time on a project, all you need to do is create a new timer, name it, then hit the clock button. From there, Hours runs in the background and tracks all your tasks. Once a task is created, you can just open the app whenever and tap it to start working. You can add as many timers as you need, and create schedules for work that send you notifications.
That's pretty much it -- Hours is very much just about tracking your time and nothing else. While you can export your hours into CSV or PDF files, there aren't any advanced visualizations or pay tracking as you'll find with an app like HoursTracker. Hours doesn't want to be that though -- it just wants to easily and quickly track your hours worked.
Hours ($6.49) [iTunes App Store]