This paper describes a Functionally-Distributed (FD) hand tracking method for hand-gesture-based wearable visual interfaces. The method is an extension of the Distributed Monte Carlo (DMC) tracking method which we have developed. The method provides coarse but rapid hand tracking results with the lowest possible number of samples on the wearable side, and can reduce latency which causes a decline in usability and performance of gesture-based interfaces. The method also provides the adaptive tracking mechanism by using the sufficient number of samples and the hand-color modeling on the infrastructure side. This paper also describes three promising applications of the hand-gesture-based wearable visual interfaces implemented on our wearable systems.