Heathcliff, the developer behind www.wp7roottools.com has now started a new site to provide root tools for Windows Phone 8.1 and Windows 10 Mobile devices. Windows Phone Internals is a new tool allows you to unlock the bootloader of select Lumia devices. After unlocking the bootloader, you can enable Root Access on the phone or create and flash Custom ROM’s. You can see a short demo of this tool above.
Root Access allows you to load your own homebrew software onto the phone with high privileges. Apps can escape from their sandboxes. The tool can also create backup-images of the phone and access the file-system in Mass Storage mode. The tool supports most versions of Windows Phone 8.1 and Windows 10 Mobile.
You can download Windows Phone Internals tool here.