A: There are many analogues to Wormhole (the first one we made) or Mystery Play (the most generic one). Some may require a token action (click your heels together to use Magic Shoes in Oz Fluxx, for example) or condition (if a certain card is in play) to activate them but they are essentially all the same kind of card.

Mystery Play in Fluxx 5.0, SE, Remixx, Astronomy, SpongeBob, and Wonderland
Mythtery Play in Fantasy
Wormhole in Star, Star Trek TOS, TNG, and Voyager
Shiny! in Firefly
Allons-y/Geronimo! in Doctor Who
Spontaneous Reaction in Chemistry
Egads! in Batman
Unknown Variable in Math
THWIP! in Marvel
(the Infinity Gauntlet Keeper in Marvel has this as its special power as well)
Great Idea! in Stoner
Magic Spell in Fairy Tale
Magic Portal in Adventure Time
Magic Shoes in Oz (if you click your heels together three times)
Open The Door in Monster (if the Spooky Door is in play)
Open A Gift! in Holiday (if The Gift is in play)
Chemical X in Cartoon Network (if at least one Powerpuff Girl is in play)
Time Doorway in Regular Show (if the Time Machine is in play)