Dialogflow - Conversational UX Platform. (ex API.ai)
Bootstrap Zero - Open-source, free Bootstrap templates collection.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Bootstrap Magic - Create your Bootstrap 4.0 themes easily with magic
Botpress - Open-source platform for developers to build high-quality digital assistants
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design