https://www.theverge.com/2017/8/30/16224876/microsoft-amazon-cortana-alexa-partnership

Amazon and Microsoft are partnering together to better integrate their Alexa and Cortana digital assistants. The New York Times reports that Alexa users will be able to access Cortana, and vice versa on a range of devices, but that the integration will be a little awkward initially. Someone using an Alexa device will have to say “Alexa, open Cortana” to get access to Microsoft’s own digital assistant, and someone using Cortana will have to say “Cortana, open Alexa.” It appears that both companies have simply created skills on each others platforms to enable the basic integration.

This cross-platform integration will also allow Alexa users to get access to some of the more unique aspects of Cortana. Microsoft has built its digital assistant to access Office products, and now Alexa will get that functionality by tapping into Cortana. While Microsoft is still tempting developers to create their own Cortana skills, existing Cortana users will be able to call up Alexa to get access to the ones that Cortana is missing.