Apple's Siri virtual assistant has been a well-used iOS feature since its introduction in 2011, and it's seemed inevitable that at some point, the company would port it (ahem - her) on over to Mac OS X. Well, according to a patent filed on Thursday, the future does indeed hold that in store. When it's going to happen is anyone's guess, although it seems highly unlikely that we'll see it anytime before OS X 10.11's release (10.10 is due sometime this fall).
Nonetheless, like Siri for iOS, this virtual assistant would always keep an ear open for commands, and then take appropriate action. At the forefront, it'd be able to interpret natural speech and result in executed commands, and also be used to retrieve data, conduct searches, and so forth. Overall, it really does seem like Siri for OS X would be little different than Siri for iOS, although the functionality will be greater due to the more advanced OS it's running in.
While it seems likely that Siri for OS X would have an always-on feature, the patent mentions that Siri could be invoked by either a touchpad or mouse gesture. There's also the option of having Siri's icon sit in the dock, with its state reflecting whether or not its listening.
One other neat feature is that based on the mouse position, Siri could better interpret exactly what you're asking for with a technique called "focus selector". Picture for example browsing through a photo gallery and wanting to change the sorting. In a more complex example, the patent lists this as a command: "Sort these by date and merge into a new document".
When using a computer, we're often focused on just a single application at a time. If we had more hands, we might be able to increase productivity. That's where "Using Digital Assistant as a Third Hand" comes in. What this would allow you to do is perform a certain action outside of the current application you're running. Imagine writing a report, for example, and without stopping your typing, say, "Hey Siri, find me a picture of (fill in the blank)". Personally, this is one feature I could really see me taking great advantage of.
Overall, I'm quite impressed with what Siri looks to be bringing to the table, and almost wish Microsoft would port Cortana over to Windows (that's assuming that something is not already in the works!).