Jar'Kai/Legends

Form X: Niman / Jar'Kai was a form of lightsaber combat

The dual saber Niman permitted a Jedi to fight with two lightsabers, one in each hand, as demonstrated by Anakin Skywalker when he first faced Count Dooku. One of the blades in the wielder's hands was used for attacking while the other one was used for defending, such as parrying, or for more offensive power. Many Jedi trained to use the Niman style in the hopes of gaining a basic knowledge of the dual-bladed attack, but very few Jedi ever totally mastered Niman. Serra Keto, Sora Bulq, Asajj Ventress, Komari Vosa, and Joclad Danva (who can be seen wielding two lightsabers in the background during the Battle of Geonosis) were practitioners of Form X; it is also possible that Darth Revan and Jedi Master Kavar may have been  masters of this form. Form X is sometimes known as Jar'Kai. (This Niman was not to be confused with the Form VI: Niman.)

For more Information on lightsaber combat, and a list of Sources see lightsaber combat.