Cue (shutdown), Don.na (pivoted), Tempo, Sunrise, Google Now, others.
Fascinating space with a lot of competition. But has any of these products gotten close to a revenue model?
Throw in some of the mail clients and other apps like Sparrow, Mailbox, and Fantastical and from the outside, it seems more like acqui-hires to absorb the product and team into a bigger company is the way to go.