This application requires root

DriveDroid allows you to boot your PC from ISO/IMG files stored on your phone. This is ideal for trying Linux distributions or always having a rescue-system on the go... without the need to burn different CDs or USB pendrives.

DriveDroid also includes a convenient menu where you can USB-images of a number of operating systems from your phone (like Mint, Ubuntu, Fedora, OpenSUSE and Arch Linux). Around 35 different systems are available at this moment.

You can also create blank USB-images which allows you to have a blank USB-drive. From your PC you can store files onto the USB-drive, but also use tools on your PC to write images to the drive.

Notes
• This application uses features of the kernel that may or may not be available/stable on your phone. Tests have shown most phones work without problems, but please keep in mind yours might not (yet) work out-of-the-box.
• Most kernels emulating USB drives, some emulating CD-rom drives and kernels with the right patches both.
• Most Linux-related ISOs can be booted from USB drives, but some ISOs can only be booted from CD-rom drives or require some kind of conversion.

Paid version
• No ads.
• Resizing of images.
• Add your own repositories. Nice for companies or groups that want to share custom or licensed images.

More info: http://softwarebakery.com/projects/drivedroid