16 projects, each with its formats, systems and licence
Open-source synthesizers now cover most of what producers pay for: wavetable engines, six-operator FM, analogue-style polysynths and deep modular-style designs. Most ship as VST3, AU and often CLAP or LV2 builds for Windows, macOS and Linux.
When you compare them, look at the licence, the formats your DAW loads and the date of the last release. Each entry here says which paid synth it is closest to, and where something is not a like-for-like swap.
Format
Activity
16 of 16
A hybrid synthesizer that mixes wavetable, FM, subtractive and modular-style routing, with a deep effects section and thousands of patches. One of the most complete free synths around.
Instead of 
Serum
Massive
A faithful six-operator FM synth modelled on the Yamaha DX7. It loads original DX7 patch banks, so decades of classic electric-piano and bell sounds work out of the box.
Instead of 
FM8
The VCV Rack modular environment packaged as a plugin, with a large bundle of modules, so you can patch a whole modular system inside your DAW.
Instead of 
Reaktor
A spectral-warping wavetable synthesizer with a clear, drag-and-drop interface, in the same league as Serum for modern wavetable sounds.
Instead of Serum
A long-running software synthesizer built on additive, subtractive and pad synthesis, known for huge evolving pads and a very large modulation system.
A semi-modular polyphonic synth with three oscillators, a flexible modulation matrix and a built-in effects chain. Good for thick leads, pads and basses.
Instead of 
Sylenth1
A physically modelled synth that rings resonators such as strings, plates and tubes, for mallet, bell and percussive tones.
Instead of 
Chromaphone
A warm analogue-style polysynth in the spirit of the classic Oberheim OB-X, maintained as the open successor to the OB-Xd project.
A virtual-analogue synth with classic oscillators, filter and envelopes plus built-in effects. Light on CPU and quick to learn.
An MPE-capable physical-modelling synth built on coupled string waveguides, made for abstract sound design.
A free emulation of the Roland TB-303 bass-line synth with the familiar acid squelch.
A two-oscillator wavetable synth with flexible modulation routing.
An eight-operator multitimbral FM synthesizer, available as a plugin and a standalone app.
A synthesizer that recreates the sound of the Roland Juno-6, Juno-60 and Juno-106, chorus included.
A pipe organ emulator using additive synthesis, available as a plugin or standalone app.
A MIDI-driven, performance-oriented synth with many oscillator and filter options and built-in effects.
