From the homepage: "Opcion font viewer is a free and open source font viewer written in Java. It allows you to view both installed and uninstalled fonts and makes selecting the right font for your project quick and easy."
See the "About" page for more information.
Opcion Font Viewer SourceForge project page
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Download the .jar version and use that.
It should act as a standalone program on any OS with the correct level of Java Installed.