synth

Surge XT open-source synthesizer plugin.

LMMS is a free cross-platform alternative to commercial programs like FL Studio®, which allow you to produce music with your computer.

Free code-based music creation and performance tool.

Virtual modular synthesizer plugin

Software modular synth

The DAW for streamers

SoundFont Midi Player is a powerful midi player/router and real time midi synth combo.

A Windows user-mode software MIDI synthesizer driver