Missing Poster is open source, and free to use. It is covered under the GNU General Public License V2, which means you can download it, us it and modify it as you see fit as long as you make the software and the source freely available for others.
Download Missing Poster installer.
This version installs on your system like standard software; it places a link in the Start menu and is useful for a computer that is used be more than one person, or for a given purpose.
Download or contribute to the source code.