Overview

Cardinal turns modular synthesis into a self-contained instrument, with 1,382 built-in modules from 84 authors or brands. That gives newcomers plenty to explore and experienced users a substantial starting point, all in a free, open-source package. But the fixed selection is a real boundary: Cardinal cannot load external modules, connect to the official Rack library or store, or accept additions to an existing build. It is a strong fit if the included modules meet your needs, not if you rely on curating a setup from third-party modules.

Key features

Variants and routing

Main, Synth, and FX plugin variants all support MIDI input and output. Main provides 8 audio inputs and outputs and 10 CV inputs and outputs, giving users the broadest specified routing option. It is unavailable in AudioUnit and VST2, and is not yet available in CLAP, so users should check format compatibility before settling on it. Mini has a small hand-picked module selection, 2 audio ports, and 5 CV ports; it is available only as LV2 and standalone. That compact option trades breadth and routing capacity for a smaller fixed setup.

Standalone control and privacy

Standalone Cardinal supports OSC remote control of patches and parameters, a useful option for remote control workflows that is not available when Cardinal runs as a plugin. The project says online access, including phone-home behavior, is disallowed for included modules and describes removing online access from the plugin and modules. Cardinal is licensed under GPLv3+.

Pricing

Free: Free. Cardinal is fully free and open-source, and its builds include the built-in modules. There are no paid tiers to unlock a larger collection; the cost of that simplicity is that users cannot add modules to an existing build. Choose it for a no-cost modular instrument if its bundled selection is enough.

Platforms

Cardinal is available on Linux, macOS, Windows, and the web. It is also offered as a standalone app, with plugin formats including AudioUnit, CLAP, LV2, VST2, and VST3. Compatibility varies by variant: Main is absent from AU and VST2 and remains unavailable in CLAP, while Mini is limited to LV2 and standalone. CLAP support is a work in progress, and VST3 plugin hosting inside Carla or Ildaeil is experimental.

Who it's for

Cardinal is aimed at musicians who want VCV Rack as a conventional open-source audio plugin, as well as users who prefer a standalone modular synth. Its module count supports exploration without assembling a collection piece by piece. Users seeking official support or a larger module collection may find Rack Pro a better fit. The maker describes Cardinal as stable, but the stated caveats around CLAP and VST3 hosting matter for users depending on those workflows. Bug reports go to GitHub, and community discussion takes place in the #cardinal IRC room on Libera.Chat.

Pros and cons

Pro: 1,382 built-in modules from 84 authors or brands make the free package substantial from the outset.
Pro: Standalone and multiple plugin formats, with MIDI input and output across Main, Synth, and FX, give users several ways to fit Cardinal into a music setup.
Pro: OSC control in standalone and the project's stated restrictions on online access address remote-control and privacy needs.
Con: The module set is fixed: no external modules, official Rack library or store access, or additions to an existing build.
Con: Variant and format limits can rule out a preferred workflow, particularly for Main in AU, VST2, or CLAP and Mini outside LV2 or standalone.

Alternatives

VCV Rack is the closest alternative for users who want an open plugin API and access to free modules rather than Cardinal's fixed bundle; VCV says Rack will remain free and open-source. For a conventional synth with a free tier and a defined preset and wavetable allowance, Vital includes full synth features, 75 presets, and 25 wavetables in its free Basic plan; its subscription is 5.00 USD per month.

Dexed is a free GPL v3 alternative for users who prefer a different free synth rather than Cardinal's modular format. Helm offers a free-or-pay-what-you-want standalone or plugin option across Linux, macOS, and Windows. Synth1 is freeware for macOS and Windows as a VSTi/AU plugin.

For a one-time purchase rather than a free modular tool, DefleMask offers a 14.99 USD one-time plan across mobile and desktop platforms; its free Legacy version is 32-bit, unsupported, and described as a demo. SynthMaster 3 is a paid synth with a free plan and trial, and suits readers considering a paid product rather than Cardinal's open-source model. Repro is a paid option for users seeking two synths in one product; it costs 149.00 EUR one time, requires host software or a DAW, and its demo emits a crackling sound.

For a broader directory of options, browse Software Synthesizers.

Verdict

Choose Cardinal if you want a free, open-source modular synth with a large built-in collection, standalone use, and plugin options. Its main advantage is how much it bundles at no cost; its main drawback is that the collection is closed to additions. If a specific outside module, official support, or a more open module ecosystem is essential, choose another tool.

	Cardinal	VPS Avenger 2
Free plan	Yes	No
Paid from	Free
Platforms	Linux, macOS, Web, Windows	macOS, Windows
Free plan	Yes	No
Synthesis engine	modular	wavetable
Plugin formats	AudioUnit, CLAP, LV2, VST2, VST3	VST2, VST3, AU, AAX
Standalone app	Yes	No
MPE support	Yes
Supported platforms		windows_macos
Included presets		750 presets

Cardinal vs VPS Avenger 2

Cardinal

VPS Avenger 2