Originally Posted by prathmann

A very simple mechanical anti-lock braking system is illustrated in the book "Bicycling Science." The rear caliper brake is mounted on a post so it can slide forward when actuated and a spring returns it to the normal position when released. The front brake cable is mounted so it's pulled by the sliding action of the rear brake rather than being controlled directly by the rider. This provides very strong front braking just until the rear wheel begins to skid a bit due to the weight shift thereby relaxing the pull of the rim on the rear brake. The article in the book indicates that the system worked very well in testing until eventually they broke the front fork due to fatigue from all the hard stops. But it did provide consistent minimum distance stops with no danger of pitch-over regardless of how hard the rider applied the brake lever.

Obviously there are some issues with this system. No ability to independently operate the front or rear brakes depending on surface conditions and also a single point of failure - if the rear brake cable snaps you lose both brakes. But it could be supplemented with the addition of a third independent brake with its own cable.