Qsynth is a fluidsynth GUI front-end application written in C++ around the Qt framework using Qt Designer. Eventually it may evolve into a softsynth management application allowing the user to control and manage a variety of command line softsynth but for the moment it wraps the excellent FluidSynth. FluidSynth is a command line software synthesiser based on the Soundfont specification.

qsynth.sourceforge.io
sourceforge.net/projects/qsynth
github.com/rncbc/qsynth
flathub.org/en/apps/org.rncbc.qsynth