It comes built into most Android phones. Google Assistant is also available for iOS devices. For instance, once Google Assistant gets to know your commuting patterns, it can provide traffic details or subway schedules before you leave the house. It is built into many Samsung phones, and can also be installed on other Android devices via an app. View at Google Play Alexa can also be downloaded and run on Android phones.
Alexa: Amazon's Alexa, which is the voice of its Echo series of products, comes with Amazon's Fire tablets and other products.
