Google Assistant and Amazon Alexa are by far the two biggest voice assistant platforms, but there are plenty of other options out there, including Apple's Siri, Samsung's Bixby, and Microsoft's Cortana. Cortana used to be limited to Microsoft's Windows 10 operating system and Microsoft's ecosystem in general, but back in late 2015, the company released apps on iOS and Android to try to catch up with the big two. It looks like Microsoft has decided there's no longer any point in offering a dedicated Cortana mobile app, however, as they've decided to discontinue the app in most markets early next year.

Microsoft has confirmed (via The Verge) they will pull support for Cortana on third-party platforms like Android and iOS on January 31st, 2020, as part of a series of changes to Cortana-related services. After this date, the app will disappear from app stores in the UK, Australia, Germany, Mexico, China, Spain, Canada, and India. Although the app will continue to work for users in the US for an undetermined amount of time after January 31st, 2020, Microsoft will no longer support the app after this date. Furthermore, an update to the Microsoft Launcher app on Android—which also had Cortana integration—will remove Cortana. Microsoft says they aren't planning on completely killing Cortana, however, as it will be integrated with the Microsoft 365 suite of productivity apps (such as Outlook). and Windows 10 will still keep it as its voice assistant.

If you use Cortana for syncing things like reminders and lists with your Windows 10 PC, you'll still be able to do so with the Microsoft To Do app which is available for free on Google Play. Else, most of your voice assistant needs can probably be fulfilled by Google Assistant, a platform that Google is completely committed to and keeps updating to get smarter by the day.

Update 1: Fully Shutting Down in 2021

Back in November, Microsoft announced they were pulling the dedicated Cortana app for Android and iOS from app stores in the UK, Australia, Germany, Mexico, China, Spain, Canada, and India. As promised, the apps were pulled from app stores in these regions on January 31st, 2020. However, the app remained accessible on iOS and Android app stores in the U.S., where it can still be downloaded to this day.

Microsoft has now announced (via The Verge) that it will shut down the current iOS and Android apps for Cortana in 2021. In addition, the company will end support for the Harman Kardon Invoke smart speaker and remove Cortana functionality from the first-generation Surface Headphones. As compensation, Microsoft is offering gift cards to owners of the Harman Kardon Invoke and first-generation Surface Headphones. More details on this program can be found here and here. Meanwhile, third-party Cortana skills will be sunset later this year on September 7, 2020, as previously announced.

Microsoft says it is focusing on improving its Microsoft 365 subscription service, but the company notes that Cortana will still be accessible in the various apps and services where it's already integrated. For example, the virtual assistant will remain in Windows 10, Outlook mobile, and will be coming to the Teams mobile app.