License: Protoreto is open-source software licensed under the GNU GPL
Protoreto is a prototyping tool that can be used to quickly create software prototypes from scratch, or based on paper prototypes, mock-up graphics, screenshots, photos, etc. User interaction can be captured, replayed and analyzed thanks to a Jacareto module. It is possible to export your Protoreto prototypes as AJAX web applications to perform online usability studies.
Other: Depends on: Java Runtime Environment, so can be launched using Java Portable and its launcher. I have the files from my Java installation on a flash drive, and made a batch file to launch Protoreto using it.
I don't know if it writes to any location aside from its own directories.
It is a useful and easy to use visual prototyper of applications or user interfaces, and it is quite unique.