A job posting popped up on Apple's website recently that alludes to Siri coming to Mac devices. The position is labeled "Siri UI Engineer" and calls for someone with experience with Unix, with a concentration in OS X.
The position must have filled quickly as the posting has been removed, but luckily it was spotted by both TechCrunch and Apple Insider. We believe that the new position would bring Siri to Mac devices as it only listed OS X development experience, and not iOS which is the only OS which Siri currently runs on.
Rumors about Siri on OS X have been abundant in recent months, and dictation software has been included in Apple's desktop OS since Mountain Lion. Other sections in the listing described close collaboration with app designers, which could mean that Siri on OS X could have expansive integration with applications as well.