ToME Wiki
The Ring of Phasing
Imbued with the screams of the victims of undead everywhere, this ring is more a hole in reality than anything else. Strange forces ripple over its surface, giving you visions of a reality considerably less solid than this one. You feel your senses reel, and must make a conscious effort not to throw this ring as far from you as possible.
It grants you the power of teleport if it is being worn. It increases your speed and luck by 15. It provides immunity to nether. It provides resistance to life draining. It renders you incorporeal. It allows you to breathe without air. It allows you to see invisible monsters. It speeds your regenerative powers. It drains experience. It cannot be harmed by acid, cold, lightning or fire.
Dropped by Tik'srvzllat. In ToME, it is the only item which renders your incorporeal simply by being worn or grants immunity to nether, and is the only artifact besides the Phial of Undeath which grants the ability to breath without air.
Chatter
DarkGod: Lol "Vanilla ToME" I guess it had to be said someday 
KhymChanur: I would have said "base ToME", but a search of the wiki showed that no-one used that term, while several people have already used "vanilla ToME".
NeilStevens: We could and should just say ToME, heh, to avoid giving the wrong impression. Modules are not ToME, they merely use the T-engine.