Ask HN: How do I build a chatbot for websites?

I have seen dozens of chatbots/NLP's SaaS which are great for integrating them into existing social channels such as Facebook Messenger, Twitter, Slack, etc. However, is there a simple solution to implement NLP such as Dialogflow or LUIS, IBM Watson for websites, which works "out of the box" in terms of cross-platform availability (Desktop: Windows IE, MacOS, Mobile: iOS, Android, and App SDK) and that is flexible in terms of UI?