Google announced iOS app indexing support the other week and yesterday they pushed it out on iOS devices when the searcher uses Chrome or the Google Search App.
This will work if you have any of the initial partner apps on your device. Specifically Eat24, Free Dictionary, Huffington Post, OpenTable, Pinterest, SeatGeek, Slideshare, Tapatalk, Yellow Pages, YouTube and Zillow in the U.S., Biblia JFA Offline and Letras in Brazil, Cookpad and Tabelog in Japan, Domain in Australia, and eBay Kleinanzeigen in Germany.
The example given by Google is a search for [I need a reservation at Bombay Cricket Club] and you'll see results from the OpenTable app.
If you do not have the app installed or there is no app indexing for the app, Google may also show recommended apps with links to download it.
Here is a search for [siddur] (name of a Jewish prayer book) on Chrome on iOS:
It doesn't show web sites with the content, it shows apps at the top. It can and probably should show more web sites but it does not, which is a bit of a big deal here.
Forum discussion at Google+.
