FluidSynth, formerly named iiwusynth, is a free open source software synthesizer which converts MIDI note data into an audio signal using SoundFont technology without need for a SoundFont-compatible soundcard.

[2] The combination of these features gives FluidSynth the following major use cases: The size of loaded SoundFont banks is limited by the amount of RAM available.

There is a GUI for FluidSynth called Qsynth, which is also open source.

[4] The core synthesizer is written as a C library with a large application programming interface (API).

It has also been converted into a LV2 plugin,[9] which has enabled it to run in LV2 plugin-based open-source effects pedals such as Mod Duo and Zynthian[10]