Meria, Scholar of Antiquity

Tap an untapped nontoken artifact you control: Add {G}.
Tap two untapped nontoken artifacts you control: Exile the top card of your library. You may play it this turn.

Unwinding Clock

Untap all artifacts you control during each other player's untap step.

Voltaic Servant

At the beginning of your end step, untap target artifact.

Genesis Chamber

Whenever a nontoken creature enters, if this artifact is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Winter Orb

As long as this artifact is untapped, players can't untap more than one land during their untap steps.