Lets user create solid green light contructs; the size, complexity, and strength of the contructs are only limited by the power levels of the ring (seen when John Steward created a construct of Xanshi), and the willpower and imagination of the user,
Can cover its user in a green energy force field. The field allows the user to fly, travel through inhospitable environments, and enter hyperspace.
Generates its user's Green Lantern uniform. The appearance of the uniform can be changed by the user.
Acts as a universal translator.
Can speak to and advise its user.
Can scan large areas for life-forms, particular targets, or an energy signature.
Can radiate electromagnetic energy of various frequencies.
Capable of generating an electrical current.
Can split atomic nucluei, manipulate subatomic particles (allowing for elemental transmutation), and can even reverse the polarity of electrons.
Can create fully-fuctioning duplicates of itself.
Can be summoned by its user over a distance (even if it it being worn by another).
Can be programmed by its user to carry out commands by itself after being removed.
Some Power Rings are genetically keyed to their user, who is then the only one who can use the ring. There are ways around this, however.
If its user if killed, then a Power Ring will automatically seek out a new user, being guided by Mogo.