https://github.com/DISTRHO/Cardinal
Cardinal is the foremost tool i use to create CV streams for my hardware modules. It takes the place of many practical and utility modules enabling me to live without the bulk and expense but not the utility or convenience of those functions in my studio. Its full recall and can be made to be interactive with proper midi input.
Cardinal is an amazing synth environment with enough depth and variety to accomplish an astonishing breadth and width of results that will surely please. Im hooked! it does FM well which im glad about, as its my favorite synth style. with over 700 modules to choose from, nobody will get to the bottom of its potential, only as far as they can take it which is the point.
Cardinal is a port of VCV rack which is its self open source. VCV rack is slightly more full featured, as you can buy brand name virtual modules to use in your patches.