Cortana is a virtual assistant created by Microsoft for Windows 10, Windows 10 Mobile, Windows Phone 8.1, Invoke smart speaker, Microsoft Band, Surface Headphones, Xbox One, iOS, Android, Windows Mixed Reality, and Amazon Alexa.
Cortana is a personal digital assistant that keeps users informed and productive, helping them get things done across devices and platforms. Skills define the tasks that Cortana can accomplish. You can extend Cortana by adding your own skills that let your users interact with your service via Cortana. Cortana invokes the skills based on input from the user, either spoken or typed.
Cortana Skills Kit https://docs.microsoft.com/en-us/cortana/skills/overview
Stack Overflow https://stackoverflow.com/questions/tagged/cortana