Microsoft has restricted the Cortana virtual assistant to Windows device thus far, but an official Android release is right around the corner. You don't have to wait, though. The beta Cortana app has leaked, and it appears to be fully functional. Just grab the app from APK Mirror and give it a shot.
After installing Cortana, you'll have to run through a quick setup process that includes agreeing to the terms and telling Cortana your name. You can also sign into your Microsoft account, assuming you have one. The app has a few Google Now-ish features with weather, news, and local destination cards. The voice features are the real selling point, though.
You can have Cortana do things like place calls, look up directions, and set calendar events just by talking. The app seems to recognize words with high accuracy and it's very snappy. Cortana is also quite good at chaining together multiple commands. For example, if you do a search for a restaurant, you can then ask it for a map or directions by saying things like, "show me a map of the second one."
Where Cortana doesn't do as well is with general information searches. Google has all the knowledge graph stuff to fall back on, but a lot of Cortana's web searches require you to scroll around and tap on the blue links. It earns points for getting the Hitchhiker's Guide question right, though.
This is still a beta app, and it's not even an official release. The version that Microsoft eventually puts in the Play Store might be a little different, but there's nothing obviously broken in this version.
- Cortana on APK Mirror