Quick Bible is a very simple, yet flexible and advanced Bible-reading app. It has a very clean material look, no ads or costs, and yet a host of useful features like multiple verse selections and notes and split-screen reading and color customization.
This is essentially a perfect emulator of a BAII Plus Calculator. Although I have a physical one too, having the same interface available on my phone anywhere is very handy. It's also free with a paid option to remove the minor ads.
The best Hacker News app I've found. It has a lot of features and customization I want and is easy to use. Among these are easy navigation, beautiful material style, and automatic day/night theming. Downsides are that you can't flag things from the app, but I've yet to find a HN app where you can do that yet, sadly. The developer recently added downvoting and unvoting, so hopefully flagging will be coming soon.
This is the best habit tracker. It's easy to use, beautiful, customizable, free, and open-source. You can set whatever habits, reminders, and frequencies you want. You can even set habits for more than once a day or track a quantity with your habit. It also makes beautiful charts of multiple types and support easy backing up and exporting of your data.