SynthFont is intended to mimic the behavior of SoundFont compatible hardware/soundcards like SoundBlaster Live! or Audigy and SynthFont is (almost) modulator aware, which Live! is not. But SynthFont is more. It provides an interface into the SoundFont structure and has basic editing capabilities. It also displays various data about the loaded MIDI file through the piano roll and the event list. Finally, there is a simple playlist feature for storing the files you are currently working on.
SynthFont also supports VST effects - there are 17 busses in all: one master bus and 16 channel busses.
VSTSynthFont (VSF), a separate VST instrument version of SynthFont is also available. It is a completely independent module, which you can use without SF installed. It does not have any of the SoundFont tools SF has, nor can it display any MIDI information as it does not handle MIDI files.