Opcion Font Viewer is a Java based font viewer that allows you to view (un)installed TrueType fonts one or many at a time. Opcion Font Viewer allows you to select and save your favourite fonts, apply font styles, and set your own sample/preview text.
I downloaded and installed this software to see if it would allow me to view all of the fonts on my system, both installed and not installed at the same time. After it took an extremely long time to install I learned that it does not have that capability, I attempted to uninstall it using the Settings\Apps functionality of Windows 10 only to have the dialogue box that said it was preparing to uninstall sit on my system for an extremely long time then close without uninstalling the application. I tried again but canceled the uninstall after it had not moved beyond preparing to uninstall for several minutes. I tried using CCleaner to uninstall it with the same results. I then attempted to use the Uninstall Opcion link in the Start menu. It took over an hour before the preparing dialogue box closed and another dialogue box asked if I really wanted to uninstall appeared. An affirmative response to this caused the Widows UAC window to appear, An affirmative response to the UAC caused another dialogue box to appear which took about 10 minutes to gather information before it finally uninstalled the app. The limited capabilities of this app and its extremely difficult and slow installation and removal process, plus the fact that the developer has ceased development of it, cause me recommend that you do not even consider trying to evaluate this app.
best linux front preview application I know of.