The "Shotoshield" was a concept armament, devised by Cassus Fett, to replace the more traditional metallic shields wielded by warriors, in order to merge defensive capability with that of attacking.
The design was simple. Cassus created a compact "mini-shotosaber" hilt, no more than 4" in length, and coated in beskar. This helt was then fixed at it's centre, to an axle protruding from a beskar plate of armour on his forearm. When activated, the blade of the mini-shoto would extend to 10" and the whole mechanism would start to rotate on the axis at over 15,000 rpm.
The result created a "shield" effect, basically derived from the lightsaber blade as it span faster than even Force-enhanced eyesight could determine. This protected the wielder from attack by blade, and even blaster bolts (however the result of such deflections were less than controlled, and would obviously return the bolt at random, rather than back to the firer of the blaster as many Force-users preferred).
The only real vulnerable point to the shotoshield was its centre, but being coated in a beskar encasing, even this "weakspot" was pretty well protected.
In addition to a handy shield, the shotoshield could also be used as a formidable weapon when desired. If the weilder could come close enough to his or her foe, merely pushing the shield against the opponent, would cause serious damage. After all, the shield itself is nothing more than a lightsaber, and as such, had the capability of causing equal amounts of damage.
The only real way past such weapon/shield, was to make use of cortosis. Only the potentially short-circuiting effects of the metal could penetrate the shield. Alternatively, removing the arm in question, perhaps by means of rpg or such projectile weaponry, was also an option.
Only Cassus Fett is known to possess such a weapon, having designed and custom built it for himself only.