Microsoft is opening up Cortana to third party device makers and developers with a Cortana Skills kit and Cortana Devices SDK.
Cortana’s Skills Kit will let developers build apps that are able to use voice commands via Cortana to enable features. The Devices SDK allows third party hardware makers build devices with Cortana on board.
Currently the Skills Kit preview is available for a few partners privately such as Expedia, TalkLocal, and Capitol One. Microsoft is working wit Harman Kardon on a new device with Cortana integration, which looks a lot like the Amazon Echo.