Android: The kernel in your operating system handles a lot of low-level tasks like managing your CPU speed. Most users will never want to touch this, but if you're a tweaker with a desire to overclock your phone, Universal Kernel Manager can be a huge help.
The app, created by XDA user apb_axel, is designed to streamline tweaking init.d scripts for different kernels. If you like to test different kernels to see which ones work best for your phone, UKM can make it much easier to switch between them. You'll also need Synapse for it to work. The app was initially designed for OnePlus devices but has now been released for all. Keep in mind, if you're not familiar with modifying your kernel, it's probably best to avoid it until after you do a fair amount of research.