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 download menu where you can download 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.
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 support emulating USB drives, some support emulating CD-rom drives and kernels with the right patches support 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.
Resizing of images.
Add your own download repositories. Nice for companies or groups that want to share custom or licensed images.
More info: http://softwarebakery.com/projects/drivedroid