Cardinal, the Rack! Cardinal is a free and open-source virtual modular synthesizer plugin, available in AudioUnit/CLAP/LV2/VST2/VST3 plugin formats and as a standalone app for FreeBSD, Linux, macOS, Windows and the Web. It is based on the popular VCV Rack but with a focus on being a fully self-contained plugin version. More specifically, this is a DPF-based plugin wrapper around VCV Rack, using its code directly instead of forking the project, with the target of having a self-contained, fully free and open-source plugin version of Rack. See the why section below for the reasons Cardinal exists, also for frequently asked questions check this FAQ document. Cardinal contains Rack, some 3rd-party modules and a few internal utilities all in a single binary. All "Core" modules from Rack have been replaced by Cardinal equivalents, simplified to better work for an audio plugin. Cardinal does not load external modules and does not connect to the official Rack library/store. All VCV branding has been removed (to the best of our knowledge) in order to avoid any trademark issues.