FSXSVC

FSX Simple Voice Control (FSXSVC) is a script for GlovePIE (freeware!) that offers a lightweight, free voice recognition capability for FSX. It basically contains a virtual co-pilot that presses keys or key combinations when you speak the appropriate command (e.g. "gear up"). It's meant to improve simulator interaction during flight phases with high workload (takeoff or landing).

It's no replacement for any payware tool (tailored to a specific aircraft like MultiCrewExperience).