I knocked up a quick NFO file viewer a few years back and just rediscovered the source.
Its written in C# under Mono, so you'll need Mono and GTK# at the very least. Check the README for details
INSTALL NOTES:
You'll need mono, mono-mcs and gtk-sharp2
To compile, change to the source directory (after extracting it) and type :-
mcs -pkg:gtk-sharp-2.0 -pkg:glade-sharp-2.0 -out:GNFOView.exe ./gtk-gui/generated.cs MainWindow.cs main.cs
USAGE NOTES:
You can pass a filename to open as a command line parameter.
In the viewer, CTRL-O to open a file, CTRL-I to invert the colours, CTRL-Q to quit. Or use the menus, its up to you.