Psychokinesis, also called PK or Telekinesis, was an ability which, in its basic form, allowed for control over matter using a Furon's capable brain. However, it also included a number of powers which were displayed in the PK Menu that was available in all Destroy All Humans! Games.
Introduced in Destroy All Humans!, Hypnotize allowed control of a human, though it's limited since the only commands were Sleep or Distract. More commands were added in certain missions, but were never used again. Variants of those commands showed up in later games.
Free Love/Disco fever: Introduced in Destroy All Humans! 2, Free Love and later Disco fever, allowed Crypto to make all Humans in the surrounding area, dance no matter what happened at the moment. It was only available for a short amount of time, but was Gene Blended/Meditated on and increased its effectiveness. While that ability was active, Crypto could Body Snatch, Kill, or Destroy anything/anyone, without the Alert Level rising.
Follow: Introduced in Destroy All Humans! 2, Follow only worked on Pedestrians, which made them mindlessly follow Crypto. Only one human was controlled at a time.
Protect: Introduced in Destroy All Humans! 2, Protect only worked on armed humans, which allowed Crypto to hypnotize a single enemy into attacking any enemies. The Gene Blender enhanced that ability and allowed enemies like the Black Ninjas, the KGB, or even Blisk Mutants to be hypnotized.
PK Magnet: Allowed the user to magnetize an object that he used PK on, which made it attract various nearby inanimate objects or people. That was very useful, when trying to collect large amounts of Brains.
Introduced in Destroy All Humans! 2, Transmogrify allowed the user to break down inanimate objects into ammunition. The Gene Blender allowed for heavier objects and vehicles to be Transmogrified. In Path of the Furon, humans were Transmogrified.
Exclusive in Destroy All Humans! 2, Mind Flash paralyzed every human on Earth or Solaris and into a temporary comatose state. Mind Flash required Crypto to consume brains in order to use it, which made Brain Extract a very useful ability.
The most powerful Furon ability, Temporal fist allowed the user to freeze time, which stopped everything else in place, allowed the user to manipulate their surroundings use a far more powerful PK Throw, and it was also used to move faster than anything else besides other users, as demonstrated in the duel between The Master and Saxon.