The Six Powers is a special, superhuman martial arts style.
The strength of a Six Powers user is measured by Doriki, which Fukuro can use his "Te-awase" to calculate with. The higher the level, the stronger each technique's potency becomes. Most of the users have their own variation of each technique, to increase their versatility and originality. Also, certain users tend to be more specialized in one technique, such as Fukuro with Soru, Jabra with Tekkai, Kaku with Rankyaku, and Rob Lucci with Shigan.
The Six Powers is the main style of combat for the World Government's secret CP9 agents, but some Marines have also demonstrated its usage. Coby used Soru against Monkey D. Luffy, Vice Admirals Momonga and Dalmatian used it to confront Luffy at Marineford, Momonga also used Geppo against Luffy, and Dalmatian also used Shigan against Luffy, Vice Admiral Vergo used it on several G-5 marines on Punk Hazard, and Captain Tashigi used it during her confrontation against Monet. The former Marines Zephyr and Binz are Six Powers users, with Zephyr being able to master it and Binz seen using at least Soru. It is unknown exactly how much the Six Powers is spread around the Marines and how widely known techniques are, but it seems the most commonly known technique is Soru.
Outside of the Marines, there are also others who learned the Rokushiki techniques, or adapt their principles to create their own, similar techniques. Monkey D. Luffy utilized his Second Gear mode to grasp the concepts of Soru, gaining an advanced version of it, while Sanji gained an advanced variant of Geppo that he can utilize both in midair and underwater.