Free & OSS Synthesizers

The free synthesizer ecosystem in 2024-26 is genuinely competitive with paid commercial synths. Surge XT, Vital, and VCV Rack alone cover most genres. For drum / sample-based instruments see audio-samplers-libraries. For guitar amp modeling see neural-amp-modeling. For DAWs that load these, see daws-overview.

All-rounder hybrid synths

• ★ Surge XT — GPL3, cross-platform. Rebooted from the closed-source 2018 Surge donation; now community-maintained. Hybrid wavetable / subtractive / FM / ring-mod with deep modulation. Ships as VST3 / AU / CLAP / LV2 + standalone. Genuinely the best free all-rounder synth.
• ★ Vital — GPL3 source / freemium binaries (Basic free, Plus / Pro paid for extra wavetables / presets). Cross-platform. Modern wavetable synth with spectral warping; rivals Serum on sound quality. Free tier is fully functional for production.
• ★ Helm — GPL3, cross-platform. Earlier project from Vital's author Matt Tytel; classic subtractive polysynth. Smaller / simpler than Vital; great pad / lead synth.

Subtractive / analog-style

• ★ OB-Xd (discoDSP) — free, cross-platform. Oberheim OB-X emulation; great for warm pads, leads, brass.
• TyrellN6 (u-he) — free, cross-platform. Polysynth co-designed with Amazona.de; classic 2-osc analog feel.
• Synth1 (Daichi Laboratory) — free Win / Mac. Ancient (2003) but still beloved; tens of thousands of presets online.
• Charlatan — free Win subtractive synth.
• Tunefish 4 — GPL spectral synth.
• Zebralette (u-he) — free single-oscillator slice of Zebra2.
• Tyrell N6, Podolski, Triple Cheese — u-he free synth lineup.

Wavetable

• ★ Vital — see above.
• Surge XT — wavetable mode is excellent.
• Helm — wavetable + subtractive.
• Wavetable (FL Studio stock) — only free if you have FL.

FM

• ★ Dexed (Digital Suburban) — GPL3, cross-platform. Yamaha DX7 FM emulation; loads original DX7 SysEx patches. The free FM synth.
• OB-Xd — has FM-ish modes via cross-mod.
• FM7 — abandoned freeware Win FM synth (cult classic).

Modular

• ★ VCV Rack 2 — GPL2 software modular synth; cross-platform. Free Rack plus thousands of free / paid 3rd-party modules. VCV Rack Pro (paid) is the same engine wrapped as a VST3 / AU / CLAP plugin to load inside a DAW.
• ★ Cardinal — GPL3, cross-platform. Clean-room VCV-based plugin (no proprietary modules) — the free DAW-pluggable VCV variant. Ships as VST3 / AU / CLAP / LV2; runs on Linux / Mac / Win and even ARM (Raspberry Pi).
• Bitwig Grid / Poly Grid — bundled with Bitwig (paid); the most powerful built-in modular environment in any DAW.
• Reaktor 6 Player (Native Instruments) — free; runs Reaktor ensembles but you can't edit them.

Physical modeling / acoustic

• AAS Player — free; loads any AAS instrument library (Strum / Lounge Lizard / Chromaphone).
• Pianoteq Stage Trial — paid (~$130+); the gold standard physical-model piano. Free demo plays for short notes only.
• Pianobook PianoBook — community-curated Decent Sampler / Kontakt patches; many free.

Drum machines / synthesis

• ★ Hydrogen — GPL, cross-platform. Pattern-based drum machine; loads Hydrogen drumkits and SFZ. Standalone + JACK.
• DrumGizmo — GPL multi-mic'd acoustic drum sampler; ships free kits (DRSKit, Muldjord). LV2 + standalone.
• MT Power Drum Kit 2 — free closed-source acoustic drums; quality very high for free.
• TAL-Drum (TAL Software) — paid sampler.
• TAL-808 — free Roland TR-808 emulation.
• Sitala (Decomposer) — free 16-pad sample drum machine; great UX.

Pads / drones / experimental

• Surge XT FX — Surge's effects shipped separately; wonderful sound design.
• Helm — pad-friendly.
• Voltage Modular Nucleus (Cherry Audio) — free 30-module subset of paid Voltage Modular.

Where to find presets

• Pianobook (free, registration) — sampler instruments.
• patchstorage (free) — VCV / Cardinal / Sonic Pi patches.
• Vital free patches — community packs everywhere.
• DX7 SysEx archives — Dexed loads them directly.

Pick this if…

• One free synth that covers everything: Surge XT.
• Modern wavetable, free tier: Vital Basic.
• DX7 / FM: Dexed.
• Modular sound design: VCV Rack 2 (standalone) or Cardinal (in a DAW).
• Free drum machine: Hydrogen.
• Vintage analog warmth, free: OB-Xd or TyrellN6.