The double-bladed lightsaber consists of an extra-long hilt with a blade at each end. According to "Jedi vs. Sith: The Essential Guide to the Force" by Ryder Windham, the double-bladed lightsaber is a dangerous weapon; it is difficult for a fighter to attack with one blade without accidentally chopping off his own limbs with the other. When used properly, however, the double-bladed lightsaber is a formidable weapon, in part because an opponent has probably not trained to fight against it.
The shoto lightsaber has a smaller handle and shorter blade than a full-sized lightsaber. Very short Jedi, such as Yoda, sometimes use shoto lightsabers because they are easier to control than longer blades. Some Jedi use shoto lightsabers as a secondary weapon; for example, Ahsoka Tano in the animated series "The Clone Wars." This fighting style (and the weapon's name) is similar to the fighting style of Japanese samurai.
The lightwhip is essentially a lightsaber with a long, flexible blade, according to the "Jedi Academy Training Manual." Like the double-bladed lightsaber, it is formidable because opponents are not used to dealing with it; but it is also dangerous simply because it is longer than a standard lightsaber. On the other hand, a lightsaber is difficult to wield and does not hit with the same deadly force as a lightsaber. Lumiya wields a lightwhip in Marvel's "Star Wars" comics and the "Legacy of the Force" novels.
The darksaber first appeared in the animated series "The Clone Wars," wielded by Mandalorian rebels. The design is closer to ancient lightsaber designs than the lightsabers that appear in the Star Wars films. It has a flat, black blade that comes to a point at the tip, similar to a real-life sword. George Lucas created the darksaber to allow for a fight between a Mandalorian and a Jedi, since ordinary weapons would be sliced in two by a lightsaber rather than blocking it.
According to the Star Wars Expanded Universe, the lightsabers seen in the Star Wars films developed over the course of thousands of years. Early lightsabers, known as protosabers, were much more unwieldy because of the need for an external power supply. A Jedi would have to connect her lightsaber hilt to a power supply via a cable, then carry the power supply at her side or back. Technological advances later allowed for smaller power cells, which could be housed in the lightsaber hilt itself.