Drift provides conversational marketing and sales software powered by both automation (rule-based) and artificial intelligence (NLP). According to their website, "Drift's conversational AI is trained on over 6 billion conversations to identify the patterns that engage and convert visitors into qualified pipeline." This means the machine learning that the chatbot comes with is already pre-trained and ready to go.
Amazon Alexa, Apple Siri, Microsoft Cortana, and Google Assistant are all, to some extent, chatbots. A chatbot is a special computer program using artificial intelligence (AI) that conducts a conversation with people, either via auditory or text input. This is precisely what you do when using Alexa and the other products mentioned. However, none of these apps are as advanced as many other chatbots – they really only give predetermined answers to questions that people ask, rather than using much AI to learn from conversations.