What is Voltage Modular?
Voltage Modular is a cross-platform, modular synthesizer for Windows and OSX in AU, VST, VST3, and Pro Tools AAX formats that also runs standalone on both platforms.
Initially a commercial app, it's now available under a freemium license with the Nucleus version bundling 22 modules being totally free. The higher tiers offer an increased number of bundled modules.
Voltage Modular Screenshots
Voltage Modular information