Tasker, on Android ($6 or so). It lets you create complex rules, using any system or environment variables, and use them to trigger various actions. One rule I have set up is when my phone is within 500 feet of the GPS coordinates of my office and it is plugged in, turn the screen to 100% brightness, never let the screen sleep, and set the ringer to vibrate. Another is when my phone is connected to a known hotspot disable GPS and 3G/4G to save batteries.
That's one nice app.
For my contracting work, I use Toggl to keep track of time. I primarily use their web interface, though they also produce desktop and mobile apps. Last time I looked at the Linux desktop app, it was lacking.
I've only bought one Android app in almost two years of owning one. It was an app to track bowling scores and statistics. I just haven't been compelled to buy anything else.
invasion app. I like it a lot for UX stuff, you can quickly build wireframes/prototypes. I feel it is a Well designed app itself and has good interface in the backend.