FluidSynth is described as 'real-time software synthesizer based on the SoundFont 2 specifications and has reached widespread distribution' and is an app in the Audio & Music category. There are more than 10 alternatives to FluidSynth for a variety of platforms, including Windows, Linux, Mac, BSD and Advanced Linux Sound Architecture. The best alternative is Qsynth, which is both free and Open Source. Other great apps like FluidSynth are ZynAddSubFX (Freemium, Open Source), yoshimi (Free, Open Source), Phasex (Free, Open Source) and Tyrell N6 (Free).
Qsynth is a simple Qt4 application wrapper for the FluidSynth software MIDI sequencer for Linux. Qsynth is a fluidsynth GUI front-end application written in C++ around the Qt4 toolkit using Qt Designer.
ZynAddSubFX is a fully featured open source software synthesizer capable of making a countless number of instruments, from some common heard from expensive hardware to interesting sounds that you'll boost to an amazing universe of sounds.
Yoshimi is a software synthesizer for Linux based on the 2.4.0 release of ZynAddSubFX, written by Nasca Octavian Paul. Yoshimi delivers the same synth capabilities, along with very good Jack and Alsa midi/audio functionality.
Tyrell is the name of a project by the German online magazine Amazona.de. A reader survey and follow-on forum posts provided a pool of ideas for a low cost HARDWARE analogue synth, which Mic 'Moogulator' Irmer used to develop quite a powerful concept.
TAL-NoiseMaker is an improved version of TAL-Elek7ro and has a completely new synth engine and a lot of improvements in sound and usability. The synth also includes a small effect section with a reverb, chorus and a simple bit crusher effect.
Zebralette is just one of Zebra2's oscillators packed into a simple, easy-to-learn framework – but you have everything you need to make some pretty amazing sounds. Sounds that can be directly loaded into Zebra2 later.