Qsynth is a FluidSynth GUI front-end application written in C++ around the Qt framework using Qt Designer. Eventually it may evolve into a soft-synth management application allowing the user to control and manage a variety of command line softsynths but for the moment it wraps the excellent FluidSynth (https://www.fluidsynth.org).
FluidSynth is a command line software synthesizer based on the Soundfont specification.
Project page: https://sourceforge.net/projects/qsynth
See also: https://www.fluidsynth.org