By Matt Vella, senior editor
FORTUNE -- Google Now, arguably the search giant's most promising mobile feature, is now available on Apple's iOS platform. An update to the Google Search app for Apple iPhones and iPads includes features found on the company's own Android operating system.
What's Google Now? Somewhat similar to Siri, the software is a digital personal assistant that answers question and collates information for its users. It can display everything from upcoming calendar appointments to the weather and sports scores. Google's (goog) assistant has some predictive abilities as well; it can, for instance, automatically remind you of your flight time and suggest the optimal time to leave your office given traffic conditions. Users can also ask Google Now questions by voice, like Apple's (aapl) Siri. Earlier this year, Amit Singhal, head of Google's core ranking team, told Fortune that Now would be getting more abilities in the future.
Google Now on iOS works much like it does on Android phones and tablets. Logging into one's Google account on the Google Search app makes the "cards" that present various types of information available. Users can swipe up for more or dismiss cards by swiping them away to the side. Voice search is available as well. Missing are cards for boarding passes and Fandango movie tickets -- those will remain under Apple's own Passbook app.
The release, rumored to be coming since earlier this year, sets up an interesting showdown between the two mobile giants. Personal assistants like Google Now and Siri are essentially high-polish gloss on top of traditional search. Controlling mobile searches -- and the ads that will eventually come with them -- will by all accounts be one of the most important revenue streams in tech going forward. Now, with Google Now and Siri living in the same device, users will effectively be able to compare the new technologies as they mature. (And one wonders what the two talking to one another might be like.)
Google Now is available for download in Apple's App Store.