Since September 11, 2001, a growing number of accessories have been developed for military rifles and machine-guns. Most of this stuff was designed for American and NATO assault rifles. But now this gear is appearing redesigned to fit AK-47s and other Russian or Chinese designed weapons.
Most of these accessories would not have appeared were it not for the development of the "Picatinny Rail." This is a standard for a metal rail, with crosswise grooves, that make mounting accessories (scopes, lights, and so on) easy to do. Just snap them on or tighten a few screws. The Picatinny Rail is a development of the Weaver Rail, which has been around since the 1930s. Items built to attach to a Weaver Rail can be attached to a Picatinny Rail but not vice versa. Anyone who handles an assault rifle or light machine-gun knows all about the Picatinny Rail and can't imagine going into combat using a rifle without rails.
Some countries and entrepreneurs have simply had Picatinny Rails created that can easily be attached to Russian or Chinese made assault rifles and machine-guns. In many countries the security forces and many criminal organizations prefer AK-47 type weapons but still want all the cool accessories. Thus the Picatinny Rail has become a common accessory itself. But manufacturers have found there is also a large market for accessories, like folding stocks, flash suppressors, and forearms grips that do not use a Picatinny Rail. These other accessories are finding a ready market all over the world. Since AK-47s are so cheap (because of all the Cold War surplus dropped on the market in the 1990s), it's not unusual to see gunmen holding tricked out AK-47s were the accessories cost far more than the rifle they are mounted on.