There are tools available to root nearly every Android phone or tablet released to date. Many of those tools require you to hook up your mobile device to a PC with a USB cable and run a utility on the PC.
Root Transmission removes the PC from the equation. You can use this app to connect two Android devices together with a USB cable and root one by sending commands across the cable.
Root Transmission requires a rooted Android device with USB On The Go (OTG) support to work. You’ll also need a USB OTG cable to link your devices.
For many users, it’s probably still simpler to just connect the device you want to root to a PC. But if you don’t have a computer handy, Root Transmission presents an interesting alternative. It also demonstrates that basically your phone or tablet is a mobile PC.
Right now the app is capable of rooting a handful of devices including the first generation Amazon Kindle Fire, Verizon Samsung Galaxy S III, international Samsung Galaxy Note II and a few more phones by running the appropriate scripts.
Bear in mind that running the wrong script can break your devices — both of them. So you’ll want to make sure you only download scripts from trusted sources and/or know how to create your own scripts before using Root Transmission.
You can find more details, download links, and instructions at the xda-developers forum.