BusyBox is an application for the Android ecosystem that provides some Unix tools, similar to what the GNU Core Utilities offer. Read more about BusyBox  

If you have a rooted device, then you will most likely be needing BusyBox, in one form or another. This is a small app designed to work specifically with the Linux kernel, which means that it’s a perfect fit for mobile devices, such as your phone. It’s also called the “"The Swiss Army Knife of Embedded Linux".
Basically, BusyBox offers users a complete environment, with all the necessary tools such as fileutils, shellutils, and so on. It’s designed to work with limited resources, which makes it ideal for mobile devices.
The developers do explain that you will need a rooted phone or tablet in order to use it. Also, it’s a fairly complex application, and it’s not what you would call user-friendly.