This is Hylek Optimized Projectile Experiment or Hope for short. It's one of the legendary weapons of Guild Wars 2: Heart of Thorns. It took actually more time to craft the pistol in game than it took me to make two of these prop weapons.
These "pistols" are huge. They have length of 73cm, but weight only 1,53kg as they are mostly made out of ABS and brass pipes. Glass pipes are made of polyester resin.
Led strips of the glass pipes are actually animated for "plasma effect", it have built in sound effects and the rotor-fan-thingy spins when powered on.