+ AA6YQ comments below
I'm using VSP Manager from K5FR. If you're a licensed ham, k5FR will send you a free copy. You could also use VSPE and there are a couple of others as well.
+ Neither of the should be used to connect two transceiver control applications to the same transceiver. They are fine for connecting Commander's Secondary CAT port to another application or to a panadapter or to a receiver.