Developers can build bots via the Microsoft Bot Framework that work in text/SMS, Office 365 mail, Teams, Skype, Slack, GroupMe, Telegram, and the web, among other platforms. Microsoft also has an Azure Bot Service, built on top of Azure Functions which is Microsoft's serverless compute service, which allows bots to scale on demand. Microsoft made the Azure Bot Service generally available in December 2017.
While Microsoft and Amazon are still promising that they will be making available the ability to access Alexa on Cortana and Cortana on Alexa, the Bot Framework bridges to the Alexa and Google Home assistants are potentially more interesting from a long-term strategy point of view to those vested in the Microsoft bot ecosystem.
Microsoft and Amazon had been aiming to enable their digital assistants to interoperate before the end of 2017, but that didn't happen. Officials haven't provided an updated timeframe as to when this will happen, but the deal seemingly is still in the cards.