Servicely (Free)
While the newest versions of Android such as Nougat are much better at power saving doze modes and preventing battery draining app wakelocks, older versions can still suffer from some heavy power drain due to apps running in the background sending notifications and syncing back to their home servers. Servicely is an aggressive task killer that runs a service every 60 seconds (configurable) and automatically kills selected applications on your kill-list, preventing excessive power drain. Users can keep Servicely on in a dedicated background thread, or set it to run only when the screen is shut off
Liveboot (Free)
Chainfire's Liveboot app does something that is really cool and potentially useful to technically oriented users. The Liveboot app uses root permissions to display the logcat and dmesg to your screen when booting your Android device. Users can configure logcat levels to display, whether to show the dmesg or not, the amount of lines to show on screen, color coding, and the option to overlay it on top of your boot animation. It also looks pretty cool if you dig a more retro command line booting look to your device's powerup cycle.
Boot Animations (Free)
Not every root app makes terribly complex technical changes to your mobile device. Sometimes, it's all about the cute cosmetic ones. Boot Animations is a free tool by JRummy Apps that can replace default Android boot up animation with a variety of choices. The app comes with more than 300 boot animations included, and can turn any animated GIF into a boot up animation. Users can preview animations, randomize the one that initiates every time you turn on your phone, or even disable animations altogether.