Area 51 is definitely one of the most curious places on the planet because of its very secretive nature.The modern name of this place is Air Force Flight Test Center,Detachment 3 or AFFTC Det.3 for short.Another popular name for this place is dreamland.This place has been used for test flying air crafts as the name says and also used as a base during the Cold War.
Now to the point about the UFO’s and the other conspiracy theories, most of sightings can be taken as the test air crafts but not all as no one outside Area 51 knows the full truth!
A few of the conspiracy theories are :
Investigation of wreckage from Rosswell.
Development of weapons and a possible link to the Majestic 12(MJ-12)
Development of alien viruses
These beliefs are made stronger by people who claimed to have been working in that place!
As seeing is believing we will not exactly the whole truth until we witness it with our own eyes!