Amazing time-management app. Use it at work. You see, how long you've worked (for example 40 hours this week, 160 hours this month). You also can export your data to CSV to process it with your computer. I recommend the commercial version. The free version has restrictions. For example, you can't see your whole data (only a few weeks back).
Moon Phase Pro
Do I need it? No.Did I buy it? Yes. Why? I don't know. It was cheap and I wanted to test the playstore. It's pretty nice if you want to see the moon phases. A nice feature is, that you can move the moon (and the time) by touching and dragging the big moon on the screen.
Because knowledge is power!