Microsoft has been working on Cortana for Android quite a bit recently. The app received a major redesign with version 2.0 in December, and added lockscreen support in March. Cortana 2.9 has just been released, which changes the UI again.
At least to me, the previous design was a bit confusing. The settings page was nestled in the user settings, and the app's functionality was split across three tabs.Read More
Cortana v2.9 changes the interface and brings back the hamburger menu [APK Download] was written by the awesome team at Android Police.