According to Reuters, Cortana could be headed to iOS and Android platforms. Microsoft released Cortana as a personal assistant for Windows Phone back in 2014, inspired by the classic Halo AI, as a way of countering Apple's own Siri for iPhone and iPad.
Now Microsoft is working on a new version for the personal assistant, based on an artificial intelligence project called "Einstein", which will be released on Windows 10 this fall. According to the Reuters the "new" Cortana will also be made available on iOS and Android platforms as a standalone app that users can purchase through the respective digital stores.
This has not yet been announced or confirmed by Microsoft, but Reuters claims to have been told about Microsoft's plans for Cortana through anonymous sources close to the project. Apparently, this is part of CEO Satya Nadella plans to make Microsoft software available on more platforms.